diff --git a/src/database.ts b/src/database.ts
index c5cf7a5d..6e370ab8 100644
--- a/src/database.ts
+++ b/src/database.ts
@@ -23,7 +23,7 @@ if (typeof writev === 'function') {
   };
 }
 
-async function exportAsync(database: Database, path: string) {
+async function exportAsync(database: Database, path: string): Promise<void> {
   const handle = await open(path, 'w');
 
   try {
@@ -79,7 +79,7 @@ interface DatabaseOptions {
 
 class Database {
   options: DatabaseOptions;
-  _models: any;
+  _models: Record<string, Model>;
   Model: typeof Model;
 
   /**
@@ -117,7 +117,7 @@ class Database {
    * @param {Schema|object} [schema]
    * @return {Model}
    */
-  model(name: string, schema?: any) {
+  model(name: string, schema?: Schema | object): Model {
     if (this._models[name]) {
       return this._models[name];
     }
@@ -133,7 +133,7 @@ class Database {
    * @param {function} [callback]
    * @return {Promise}
    */
-  load(callback?) {
+  load(callback?: NodeJSLikeCallback<any>): Bluebird<any> {
     const { path, onUpgrade, onDowngrade, version: newVersion } = this.options;
 
     if (!path) throw new WarehouseError('options.path is required');
@@ -173,14 +173,14 @@ class Database {
    * @param {function} [callback]
    * @return {Promise}
    */
-  save(callback?) {
+  save(callback?: NodeJSLikeCallback<any>): Bluebird<void>{
     const { path } = this.options;
 
     if (!path) throw new WarehouseError('options.path is required');
     return Bluebird.resolve(exportAsync(this, path)).asCallback(callback);
   }
 
-  toJSON() {
+  toJSON(): { meta: { version: number, warehouse: string }, models: Record<string, Model> } {
     const models = Object.keys(this._models)
       .reduce((obj, key) => {
         const value = this._models[key];
diff --git a/src/document.ts b/src/document.ts
index 2c23b2e5..fd4a7401 100644
--- a/src/document.ts
+++ b/src/document.ts
@@ -1,17 +1,20 @@
 import rfdc from 'rfdc';
+import type Model from './model';
+import type Schema from './schema';
 const cloneDeep = rfdc();
 
 abstract class Document {
-  abstract _model;
-  _id!: any;
-  abstract _schema;
+  abstract _model: Model;
+  _id!: string | number | undefined;
+  abstract _schema: Schema;
+  [key: PropertyKey]: any;
 
   /**
    * Document constructor.
    *
    * @param {object} data
    */
-  constructor(data) {
+  constructor(data?: object) {
     if (data) {
       Object.assign(this, data);
     }
@@ -23,7 +26,7 @@ abstract class Document {
    * @param {function} [callback]
    * @return {Promise}
    */
-  save(callback) {
+  save(callback?: NodeJSLikeCallback<any>): Promise<any> {
     return this._model.save(this, callback);
   }
 
@@ -34,7 +37,7 @@ abstract class Document {
    * @param {function} [callback]
    * @return {Promise}
    */
-  update(data, callback) {
+  update(data: Record<string, any>, callback?: NodeJSLikeCallback<any>): Promise<any> {
     return this._model.updateById(this._id, data, callback);
   }
 
@@ -45,7 +48,7 @@ abstract class Document {
    * @param {function} [callback]
    * @return {Promise}
    */
-  replace(data, callback) {
+  replace(data: object | Document, callback?: NodeJSLikeCallback<any>): Promise<any> {
     return this._model.replaceById(this._id, data, callback);
   }
 
@@ -55,7 +58,7 @@ abstract class Document {
    * @param {function} [callback]
    * @return {Promise}
    */
-  remove(callback) {
+  remove(callback?: NodeJSLikeCallback<any>): Promise<any> {
     return this._model.removeById(this._id, callback);
   }
 
@@ -64,7 +67,7 @@ abstract class Document {
    *
    * @return {object}
    */
-  toObject() {
+  toObject(): object {
     const keys = Object.keys(this);
     const obj = {};
 
@@ -83,7 +86,7 @@ abstract class Document {
    *
    * @return {String}
    */
-  toString() {
+  toString(): string {
     return JSON.stringify(this);
   }
 
@@ -93,13 +96,13 @@ abstract class Document {
    * @param {String|Object} expr
    * @return {Document}
    */
-  populate(expr) {
+  populate(expr: string | any[] | { path?: string; model?: any; [key: PropertyKey]: any }): Document {
     const stack = this._schema._parsePopulate(expr);
     return this._model._populate(this, stack);
   }
 }
 
-function isGetter(obj, key) {
+function isGetter(obj: any, key: PropertyKey): any {
   return Object.getOwnPropertyDescriptor(obj, key).get;
 }
 
diff --git a/src/lib/jsonstream/index.ts b/src/lib/jsonstream/index.ts
index e028660b..9a5dbf2f 100644
--- a/src/lib/jsonstream/index.ts
+++ b/src/lib/jsonstream/index.ts
@@ -7,7 +7,7 @@ import Parser from 'jsonparse';
  * @param {*} y
  * @returns {boolean}
  */
-const check = (x, y) => {
+const check = (x, y): boolean => {
   if (typeof x === 'string') {
     return y === x;
   }
@@ -27,7 +27,7 @@ const check = (x, y) => {
   return false;
 };
 
-export function parse(path, map = null) {
+export function parse(path: string | any[], map = null) {
   let header, footer;
 
   const parser = new Parser();
diff --git a/src/model.ts b/src/model.ts
index ea3e4ffa..3f9a0d88 100644
--- a/src/model.ts
+++ b/src/model.ts
@@ -10,26 +10,27 @@ import * as Types from './types/index';
 import WarehouseError from './error';
 import PopulationError from './error/population';
 import Mutex from './mutex';
+import type Database from './database';
 
 class Model extends EventEmitter {
   _mutex = new Mutex();
-  data: Record<any, any> = {};
-  schema;
+  data: Record<PropertyKey, any> = {};
+  schema: Schema;
   length = 0;
   Document;
   Query;
-  _database;
+  _database: Database;
 
   /**
    * Model constructor.
    *
    * @param {string} name Model name
-   * @param {Schema|object} [schema] Schema
+   * @param {Schema|object} [schema_] Schema
    */
-  constructor(public name: string, schema_) {
+  constructor(public name: string, schema_: Schema | object) {
     super();
 
-    let schema;
+    let schema: Schema;
 
     // Define schema
     if (schema_ instanceof Schema) {
@@ -50,7 +51,7 @@ class Model extends EventEmitter {
     class _Document extends Document {
       _model!: Model;
       _schema!: Schema;
-      constructor(data) {
+      constructor(data: object) {
         super(data);
 
         // Apply getters
@@ -86,7 +87,7 @@ class Model extends EventEmitter {
    * @param {object} data
    * @return {Document}
    */
-  new(data) {
+  new(data?: object): Document {
     return new this.Document(data);
   }
 
@@ -98,7 +99,7 @@ class Model extends EventEmitter {
    *   @param {boolean} [options.lean=false] Returns a plain JavaScript object
    * @return {Document|object}
    */
-  findById(id, options_?) {
+  findById(id: PropertyKey, options_?: Options): Document | Record<PropertyKey, any> {
     const raw = this.data[id];
     if (!raw) return;
 
@@ -116,7 +117,7 @@ class Model extends EventEmitter {
    * @param {*} id
    * @return {boolean}
    */
-  has(id) {
+  has(id: PropertyKey): boolean {
     return Boolean(this.data[id]);
   }
 
@@ -143,11 +144,11 @@ class Model extends EventEmitter {
    * @return {Promise}
    * @private
    */
-  _insertOne(data_) {
+  _insertOne(data_: Document | object): Promise<any> {
     const schema = this.schema;
 
     // Apply getters
-    const data = data_ instanceof this.Document ? data_ : this.new(data_);
+    const data = (data_ instanceof this.Document ? data_ : this.new(data_)) as Document;
     const id = data._id;
 
     // Check ID
@@ -181,7 +182,7 @@ class Model extends EventEmitter {
    * @param {function} [callback]
    * @return {Promise}
    */
-  insertOne(data, callback?) {
+  insertOne(data: Document | object, callback?: NodeJSLikeCallback<any>): Promise<any> {
     return Promise.using(this._acquireWriteLock(), () => this._insertOne(data)).asCallback(callback);
   }
 
@@ -192,7 +193,7 @@ class Model extends EventEmitter {
    * @param {function} [callback]
    * @return {Promise}
    */
-  insert(data, callback) {
+  insert(data: object | object[], callback?: NodeJSLikeCallback<any>): Promise<any> {
     if (Array.isArray(data)) {
       return Promise.mapSeries(data, item => this.insertOne(item)).asCallback(callback);
     }
@@ -207,8 +208,8 @@ class Model extends EventEmitter {
    * @param {function} [callback]
    * @return {Promise}
    */
-  save(data, callback) {
-    const id = data._id;
+  save(data: Document | object, callback?: NodeJSLikeCallback<any>): Promise<any> {
+    const id = (data as any)._id;
 
     if (!id) return this.insertOne(data, callback);
 
@@ -229,7 +230,7 @@ class Model extends EventEmitter {
    * @return {Promise}
    * @private
    */
-  _updateWithStack(id, stack): Promise<any> {
+  _updateWithStack(id: string | number, stack: any[]): Promise<any> {
     const schema = this.schema;
 
     const data = this.data[id];
@@ -271,7 +272,7 @@ class Model extends EventEmitter {
    * @param {function} [callback]
    * @return {Promise}
    */
-  updateById(id, update, callback?) {
+  updateById(id: string | number, update: Record<string, any>, callback?: NodeJSLikeCallback<any>): Promise<any> {
     return Promise.using(this._acquireWriteLock(), () => {
       const stack = this.schema._parseUpdate(update);
       return this._updateWithStack(id, stack);
@@ -286,8 +287,8 @@ class Model extends EventEmitter {
    * @param {function} [callback]
    * @return {Promise}
    */
-  update(query, data, callback?) {
-    return this.find(query).update(data, callback);
+  update(query: object, data: object, callback?: NodeJSLikeCallback<any>): Promise<any> {
+    return (this.find(query) as Query).update(data, callback);
   }
 
   /**
@@ -298,17 +299,17 @@ class Model extends EventEmitter {
    * @return {Promise}
    * @private
    */
-  _replaceById(id, data_) {
+  _replaceById(id: string | number, data_: Document | object): Promise<any> {
     const schema = this.schema;
 
     if (!this.has(id)) {
       return Promise.reject(new WarehouseError('ID `' + id + '` does not exist', WarehouseError.ID_NOT_EXIST));
     }
 
-    data_._id = id;
+    (data_ as any)._id = id;
 
     // Apply getters
-    const data = data_ instanceof this.Document ? data_ : this.new(data_);
+    const data = (data_ instanceof this.Document ? data_ : this.new(data_)) as Document;
 
     // Apply setters
     const result = data.toObject();
@@ -332,7 +333,7 @@ class Model extends EventEmitter {
    * @param {function} [callback]
    * @return {Promise}
    */
-  replaceById(id, data, callback?) {
+  replaceById(id: string | number, data: Document | object, callback?: NodeJSLikeCallback<any>): Promise<any> {
     return Promise.using(this._acquireWriteLock(), () => this._replaceById(id, data)).asCallback(callback);
   }
 
@@ -344,19 +345,18 @@ class Model extends EventEmitter {
    * @param {function} [callback]
    * @return {Promise}
    */
-  replace(query, data, callback?) {
-    return this.find(query).replace(data, callback);
+  replace(query: object, data, callback?: NodeJSLikeCallback<any>): Promise<any> {
+    return (this.find(query) as Query).replace(data, callback);
   }
 
   /**
    * Finds a document by its identifier and remove it.
    *
    * @param {*} id
-   * @param {function} [callback]
    * @return {Promise}
    * @private
    */
-  _removeById(id) {
+  _removeById(id: string | number): Promise<any> {
     const schema = this.schema;
 
     const data = this.data[id];
@@ -383,7 +383,7 @@ class Model extends EventEmitter {
    * @param {function} [callback]
    * @return {Promise}
    */
-  removeById(id, callback) {
+  removeById(id: string | number, callback?: NodeJSLikeCallback<any>): Promise<any> {
     return Promise.using(this._acquireWriteLock(), () => this._removeById(id)).asCallback(callback);
   }
 
@@ -391,17 +391,17 @@ class Model extends EventEmitter {
    * Removes matching documents.
    *
    * @param {object} query
-   * @param {object} [callback]
+   * @param {function} [callback]
    * @return {Promise}
    */
-  remove(query, callback) {
-    return this.find(query).remove(callback);
+  remove(query: object, callback?: NodeJSLikeCallback<any>): Promise<any> {
+    return (this.find(query) as Query).remove(callback);
   }
 
   /**
    * Deletes a model.
    */
-  destroy() {
+  destroy(): void {
     this._database._models[this.name] = null;
   }
 
@@ -410,7 +410,7 @@ class Model extends EventEmitter {
    *
    * @return {number}
    */
-  count() {
+  count(): number {
     return this.length;
   }
 
@@ -420,7 +420,7 @@ class Model extends EventEmitter {
    * @param {function} iterator
    * @param {object} [options] See {@link Model#findById}.
    */
-  forEach(iterator, options?) {
+  forEach(iterator: (value: any, index: number) => any, options?: Options): void {
     const keys = Object.keys(this.data);
     let num = 0;
 
@@ -436,7 +436,7 @@ class Model extends EventEmitter {
    * @param {Object} [options] See {@link Model#findById}.
    * @return {Array}
    */
-  toArray(options?) {
+  toArray(options?: Options): any[] {
     const result = new Array(this.length);
 
     this.forEach((item, i) => {
@@ -456,7 +456,7 @@ class Model extends EventEmitter {
    *   @param {Boolean} [options.lean=false] Returns a plain JavaScript object.
    * @return {Query|Array}
    */
-  find(query, options: { limit?: number; skip?: number; lean?: boolean; } = {}) {
+  find(query: object, options: Options = {}): Query | any[] {
     const filter = this.schema._execQuery(query);
     const keys = Object.keys(this.data);
     const len = keys.length;
@@ -491,11 +491,11 @@ class Model extends EventEmitter {
    *   @param {Boolean} [options.lean=false] Returns a plain JavaScript object.
    * @return {Document|Object}
    */
-  findOne(query, options_ : { skip?: number; lean?: boolean; } = {}) {
+  findOne(query: object, options_ : Options = {}): Document | Record<PropertyKey, any> {
     const options = Object.assign(options_, { limit: 1 });
 
     const result = this.find(query, options);
-    return options.lean ? result[0] : result.data[0];
+    return options.lean ? (result as any[])[0] : (result as Query).toArray()[0];
   }
 
   /**
@@ -505,7 +505,7 @@ class Model extends EventEmitter {
    * @param {String|Number} [order]
    * @return {Query}
    */
-  sort(orderby, order) {
+  sort(orderby: string | object, order?: string | number): Query {
     const sort = parseArgs(orderby, order);
     const fn = this.schema._execSort(sort);
 
@@ -520,7 +520,7 @@ class Model extends EventEmitter {
    * @param {Object} [options] See {@link Model#findById}.
    * @return {Document|Object}
    */
-  eq(i_, options?) {
+  eq(i_: number, options?: Options): Document | Record<PropertyKey, any> {
     let index = i_ < 0 ? this.length + i_ : i_;
     const data = this.data;
     const keys = Object.keys(data);
@@ -545,7 +545,7 @@ class Model extends EventEmitter {
    * @param {Object} [options] See {@link Model#findById}.
    * @return {Document|Object}
    */
-  first(options) {
+  first(options?: Options): Document | Record<PropertyKey, any> {
     return this.eq(0, options);
   }
 
@@ -555,7 +555,7 @@ class Model extends EventEmitter {
    * @param {Object} [options] See {@link Model#findById}.
    * @return {Document|Object}
    */
-  last(options) {
+  last(options?: Options): Document | Record<PropertyKey, any> {
     return this.eq(-1, options);
   }
 
@@ -566,7 +566,7 @@ class Model extends EventEmitter {
    * @param {Number} [end]
    * @return {Query}
    */
-  slice(start_: number, end_?: number) {
+  slice(start_?: number, end_?: number): Query {
     const total = this.length;
 
     let start = start_ | 0;
@@ -605,7 +605,7 @@ class Model extends EventEmitter {
    * @param {Number} i
    * @return {Query}
    */
-  limit(i) {
+  limit(i: number): Query {
     return this.slice(0, i);
   }
 
@@ -615,7 +615,7 @@ class Model extends EventEmitter {
    * @param {Number} i
    * @return {Query}
    */
-  skip(i) {
+  skip(i: number): Query {
     return this.slice(i);
   }
 
@@ -624,7 +624,7 @@ class Model extends EventEmitter {
    *
    * @return {Query}
    */
-  reverse() {
+  reverse(): Query {
     return new this.Query(this.toArray().reverse());
   }
 
@@ -633,7 +633,7 @@ class Model extends EventEmitter {
    *
    * @return {Query}
    */
-  shuffle() {
+  shuffle(): Query {
     return new this.Query(shuffle(this.toArray()));
   }
 
@@ -644,7 +644,7 @@ class Model extends EventEmitter {
    * @param {Object} [options]
    * @return {Array}
    */
-  map(iterator, options) {
+  map<T>(iterator: (value: any, index: number) => T, options?: Options): T[] {
     const result = new Array(this.length);
     const keys = Object.keys(this.data);
     const len = keys.length;
@@ -668,10 +668,10 @@ class Model extends EventEmitter {
    * @param {*} [initial] By default, the initial value is the first document.
    * @return {*}
    */
-  reduce(iterator, initial) {
+  reduce<T>(iterator: (pre: any, cur: any, index: number) => T, initial?: T): T {
     const arr = this.toArray();
     const len = this.length;
-    let i, result;
+    let i: number, result: any;
 
     if (initial === undefined) {
       i = 1;
@@ -696,7 +696,7 @@ class Model extends EventEmitter {
    * @param {*} [initial] By default, the initial value is the last document.
    * @return {*}
    */
-  reduceRight(iterator, initial) {
+  reduceRight<T>(iterator: (pre: any, cur: any, index: number) => T, initial?: T): T {
     const arr = this.toArray();
     const len = this.length;
     let i, result;
@@ -724,10 +724,10 @@ class Model extends EventEmitter {
    * @param {Object} [options]
    * @return {Query}
    */
-  filter(iterator, options) {
+  filter(iterator: (value: any, index: number) => any, options?: Options): Query {
     const arr = [];
 
-    this.forEach((item, i) => {
+    this.forEach((item: any, i: number) => {
       if (iterator(item, i)) arr.push(item);
     }, options);
 
@@ -741,7 +741,7 @@ class Model extends EventEmitter {
    * @param {Function} iterator
    * @return {Boolean}
    */
-  every(iterator) {
+  every(iterator: (value: any, index: number) => any): boolean {
     const keys = Object.keys(this.data);
     const len = keys.length;
     let num = 0;
@@ -766,7 +766,7 @@ class Model extends EventEmitter {
    * @param {Function} iterator
    * @return {Boolean}
    */
-  some(iterator) {
+  some(iterator: (value: any, index: number) => any): boolean {
     const keys = Object.keys(this.data);
     const len = keys.length;
     let num = 0;
@@ -793,9 +793,9 @@ class Model extends EventEmitter {
    * @return {Function}
    * @private
    */
-  _populateGetter(data, model, options) {
+  _populateGetter(data: string | number, model: Model, options: unknown) {
     let hasCache = false;
-    let cache;
+    let cache: Record<PropertyKey, any> | Document;
 
     return () => {
       if (!hasCache) {
@@ -816,10 +816,10 @@ class Model extends EventEmitter {
    * @return {Function}
    * @private
    */
-  _populateGetterArray(data, model, options) {
+  _populateGetterArray(data: any[], model: Model, options: Options): () => any[] | Query {
     const Query = model.Query;
     let hasCache = false;
-    let cache;
+    let cache: any[] | Query;
 
     return () => {
       if (!hasCache) {
@@ -830,7 +830,7 @@ class Model extends EventEmitter {
         }
 
         if (options.match) {
-          cache = new Query(arr).find(options.match, options);
+          cache = (new Query(arr) as Query).find(options.match, options);
         } else if (options.skip) {
           if (options.limit) {
             arr = arr.slice(options.skip, options.skip + options.limit);
@@ -864,7 +864,7 @@ class Model extends EventEmitter {
    * @return {Object}
    * @private
    */
-  _populate(data, stack) {
+  _populate(data: Document, stack: any[]): Document {
     const models = this._database._models;
 
     for (let i = 0, len = stack.length; i < len; i++) {
@@ -894,7 +894,7 @@ class Model extends EventEmitter {
    * @param {String|Object} path
    * @return {Query}
    */
-  populate(path) {
+  populate(path: string | any[] | { path?: string; model?: any; [key: PropertyKey]: any }): Query {
     if (!path) throw new TypeError('path is required');
 
     const stack = this.schema._parsePopulate(path);
@@ -913,7 +913,7 @@ class Model extends EventEmitter {
    * @param {Array} arr
    * @private
    */
-  _import(arr) {
+  _import(arr: any[]) {
     const len = arr.length;
     const data = this.data;
     const schema = this.schema;
@@ -932,11 +932,11 @@ class Model extends EventEmitter {
    * @return {String}
    * @private
    */
-  _export() {
+  _export(): string {
     return JSON.stringify(this.toJSON());
   }
 
-  toJSON() {
+  toJSON(): any[] {
     const result = new Array(this.length);
     const { data, schema } = this;
     const keys = Object.keys(data);
@@ -958,7 +958,7 @@ class Model extends EventEmitter {
 
 Model.prototype.get = Model.prototype.findById;
 
-function execHooks(schema, type, event, data) {
+function execHooks(schema: Schema, type: string, event: string, data: any): Promise<any> {
   const hooks = schema.hooks[type][event] as ((data: any) => Promise<void> | void)[];
   if (!hooks.length) return Promise.resolve(data);
 
diff --git a/src/mutex.ts b/src/mutex.ts
index 6eaa0ab4..dec0dbea 100644
--- a/src/mutex.ts
+++ b/src/mutex.ts
@@ -6,7 +6,7 @@ class Mutex {
     this._queue = [];
   }
 
-  lock(fn: () => void) {
+  lock(fn: () => void): void {
     if (this._locked) {
       this._queue.push(fn);
       return;
@@ -16,7 +16,7 @@ class Mutex {
     fn();
   }
 
-  unlock() {
+  unlock(): void {
     if (!this._locked) return;
 
     const next = this._queue.shift();
diff --git a/src/query.ts b/src/query.ts
index 0eb8fae4..8a54adba 100644
--- a/src/query.ts
+++ b/src/query.ts
@@ -1,17 +1,22 @@
 import Promise from 'bluebird';
 import { parseArgs, shuffle } from './util';
+import type Model from './model';
+import type Schema from './schema';
+import type Document from './document';
 
 abstract class Query {
+  data: any[];
   length: number;
-  abstract _model;
-  abstract _schema;
+  abstract _model: Model;
+  abstract _schema: Schema;
 
   /**
    * Query constructor.
    *
    * @param {Array} data
    */
-  constructor(private data: any[]) {
+  constructor(data: any[]) {
+    this.data = data;
     this.length = data.length;
   }
 
@@ -53,7 +58,7 @@ abstract class Query {
    * @param {Number} i
    * @return {Document|Object}
    */
-  eq(i: number) {
+  eq(i: number): Document | Record<PropertyKey, any> {
     const index = i < 0 ? this.length + i : i;
     return this.data[index];
   }
@@ -63,7 +68,7 @@ abstract class Query {
    *
    * @return {Document|Object}
    */
-  first() {
+  first(): Document | Record<PropertyKey, any> {
     return this.eq(0);
   }
 
@@ -72,7 +77,7 @@ abstract class Query {
    *
    * @return {Document|Object}
    */
-  last() {
+  last(): Document | Record<PropertyKey, any> {
     return this.eq(-1);
   }
 
@@ -135,7 +140,7 @@ abstract class Query {
    *   @param {Boolean} [options.lean=false] Returns a plain JavaScript object.
    * @return {Query|Array}
    */
-  find(query: any, options: { limit?: number; skip?: number; lean?: boolean; } = {}): any[] | Query {
+  find(query: object, options: Options = {}): any[] | Query {
     const filter = this._schema._execQuery(query);
     const { data, length } = this;
     const { lean = false } = options;
@@ -167,7 +172,7 @@ abstract class Query {
    *   @param {Boolean} [options.lean=false] Returns a plain JavaScript object.
    * @return {Document|Object}
    */
-  findOne(query: any, options: { skip?: number; lean?: boolean; } = {}): any {
+  findOne(query: object, options: Options = {}): Document | Record<PropertyKey, any> {
     const _options = Object.assign(options, { limit: 1 });
 
     const result = this.find(query, _options);
@@ -192,7 +197,7 @@ abstract class Query {
    * @param {String|Number} [order]
    * @return {Query}
    */
-  sort(orderby, order): Query {
+  sort(orderby: string | object, order?: string | number | object): Query {
     const sort = parseArgs(orderby, order);
     const fn = this._schema._execSort(sort);
 
@@ -224,9 +229,9 @@ abstract class Query {
    * @param {*} [initial] By default, the initial value is the first document.
    * @return {*}
    */
-  reduce(iterator, initial?) {
+  reduce<T>(iterator: (pre: any, cur: any, index: number) => T, initial?: T): T {
     const { data, length } = this;
-    let result, i;
+    let result: T, i: number;
 
     if (initial === undefined) {
       i = 1;
@@ -251,7 +256,7 @@ abstract class Query {
    * @param {*} [initial] By default, the initial value is the last document.
    * @return {*}
    */
-  reduceRight(iterator, initial?) {
+  reduceRight<T>(iterator: (pre: any, cur: any, index: number) => T, initial?: T): T {
     const { data, length } = this;
     let result, i;
 
@@ -330,7 +335,7 @@ abstract class Query {
    * @param {Function} [callback]
    * @return {Promise}
    */
-  update(data: any, callback?: (err?: any) => void): Promise<any> {
+  update(data: any, callback?: NodeJSLikeCallback<any>): Promise<any> {
     const model = this._model;
     const stack = this._schema._parseUpdate(data);
 
@@ -344,7 +349,7 @@ abstract class Query {
    * @param {Function} [callback]
    * @return {Promise}
    */
-  replace(data: any, callback?: (err?: any) => void): Promise<any> {
+  replace(data: any, callback?: NodeJSLikeCallback<any>): Promise<any> {
     const model = this._model;
 
     return Promise.map(this.data, item => model.replaceById(item._id, data)).asCallback(callback);
@@ -356,7 +361,7 @@ abstract class Query {
    * @param {Function} [callback]
    * @return {Promise}
    */
-  remove(callback) {
+  remove(callback?: NodeJSLikeCallback<any>): Promise<any> {
     const model = this._model;
 
     return Promise.mapSeries(this.data, item => model.removeById(item._id)).asCallback(callback);
@@ -368,7 +373,7 @@ abstract class Query {
    * @param {String|Object} expr
    * @return {Query}
    */
-  populate(expr: any): Query {
+  populate(expr: string | any[] | { path?: string; model?: any; [key: PropertyKey]: any }): Query {
     const stack = this._schema._parsePopulate(expr);
     const { data, length } = this;
     const model = this._model;
diff --git a/src/schema.ts b/src/schema.ts
index f9f81590..e6c54840 100644
--- a/src/schema.ts
+++ b/src/schema.ts
@@ -11,12 +11,14 @@ import { isPlainObject } from 'is-plain-object';
  * @param {*} data
  * @return {boolean}
  */
+type queryFilterCallback = (data: unknown) => boolean;
 
 /**
  * @callback queryCallback
  * @param {*} data
  * @return {void}
  */
+type queryCallback = (data: unknown) => void;
 
 /**
  * @callback queryParseCallback
@@ -24,16 +26,21 @@ import { isPlainObject } from 'is-plain-object';
  * @param {*} b
  * @returns {*}
  */
+type queryParseCallback = (a: unknown, b: unknown) => number;
 
 /**
  * @typedef PopulateResult
  * @property {string} path
  * @property {*} model
  */
+type PopulateResult = {
+  path: string;
+  model: any;
+};
 
 const builtinTypes = new Set(['String', 'Number', 'Boolean', 'Array', 'Object', 'Date', 'Buffer']);
 
-const getSchemaType = (name, options) => {
+const getSchemaType = (name: string, options: Record<string, unknown> | { type: any; }) => {
   const Type = options.type || options;
   const typeName = Type.name;
 
@@ -44,13 +51,14 @@ const getSchemaType = (name, options) => {
   return new Type(name, options);
 };
 
-const checkHookType = type => {
+const checkHookType = (type: string) => {
   if (type !== 'save' && type !== 'remove') {
     throw new TypeError('Hook type must be `save` or `remove`!');
   }
 };
 
-const hookWrapper = fn => {
+const hookWrapper = (fn: (callback: NodeJSLikeCallback<any>, options?: Promise.PromisifyOptions) => void)
+  : (callback?: NodeJSLikeCallback<any, any>) => Promise<any> => {
   if (fn.length > 1) {
     return Promise.promisify(fn);
   }
@@ -61,10 +69,10 @@ const hookWrapper = fn => {
 /**
  * @param {Function[]} stack
  */
-const execSortStack = stack => {
+const execSortStack = (stack: Function[]) => {
   const len = stack.length;
 
-  return (a, b) => {
+  return (a: any, b: any) => {
     let result;
 
     for (let i = 0; i < len; i++) {
@@ -76,32 +84,32 @@ const execSortStack = stack => {
   };
 };
 
-const sortStack = (path_, key, sort) => {
+const sortStack = (path_: SchemaType<any>, key: string, sort: string | number) => {
   const path = path_ || new SchemaType(key);
   const descending = sort === 'desc' || sort === -1;
 
-  return (a, b) => {
+  return (a: any, b: any) => {
     const result = path.compare(getProp(a, key), getProp(b, key));
     return descending && result ? result * -1 : result;
   };
 };
 
 class UpdateParser {
-  static updateStackNormal(key, update) {
-    return data => { setProp(data, key, update); };
+  static updateStackNormal(key: string, update: any) {
+    return (data: any) => { setProp(data, key, update); };
   }
 
-  static updateStackOperator(path_, ukey, key, update) {
+  static updateStackOperator(path_: SchemaType<unknown>, ukey: string | number, key: string, update: any) {
     const path = path_ || new SchemaType(key);
 
-    return data => {
+    return (data: any) => {
       const result = path[ukey](getProp(data, key), update, data);
       setProp(data, key, result);
     };
   }
 
   // eslint-disable-next-line no-useless-constructor
-  constructor(private paths) {}
+  constructor(private paths: Record<string, SchemaType<any>>) { }
 
   /**
    * Parses updating expressions and returns a stack.
@@ -110,11 +118,11 @@ class UpdateParser {
    * @param {queryCallback[]} [stack]
    * @private
    */
-  parseUpdate(updates, prefix = '', stack = []) {
+  parseUpdate(updates: object, prefix = '', stack: queryCallback[] = []): queryCallback[] {
     const { paths } = this;
     const { updateStackOperator } = UpdateParser;
     const keys = Object.keys(updates);
-    let path, prefixNoDot;
+    let path: SchemaType<any>, prefixNoDot: string;
 
     if (prefix) {
       prefixNoDot = prefix.substring(0, prefix.length - 1);
@@ -158,7 +166,7 @@ class UpdateParser {
  */
 class QueryParser {
   // eslint-disable-next-line no-useless-constructor
-  constructor(private paths) {}
+  constructor(private paths: Record<string, SchemaType<any>>) { }
 
   /**
    *
@@ -166,10 +174,10 @@ class QueryParser {
    * @param {*} query
    * @return {queryFilterCallback}
    */
-  queryStackNormal(name, query) {
+  queryStackNormal(name: string, query: unknown): queryFilterCallback {
     const path = this.paths[name] || new SchemaType(name);
 
-    return data => path.match(getProp(data, name), query, data);
+    return (data: unknown) => path.match(getProp(data, name), query, data);
   }
 
   /**
@@ -179,7 +187,7 @@ class QueryParser {
    * @param {*} query
    * @return {queryFilterCallback}
    */
-  queryStackOperator(qkey, name, query) {
+  queryStackOperator(qkey: string, name: string, query: any): queryFilterCallback {
     const path = this.paths[name] || new SchemaType(name);
 
     return data => path[qkey](getProp(data, name), query, data);
@@ -191,7 +199,7 @@ class QueryParser {
    * @return {void}
    * @private
    */
-  $and(arr, stack) {
+  $and(arr: any[], stack: queryFilterCallback[]): void {
     for (let i = 0, len = arr.length; i < len; i++) {
       stack.push(this.execQuery(arr[i]));
     }
@@ -202,7 +210,7 @@ class QueryParser {
    * @return {queryFilterCallback}
    * @private
    */
-  $or(query) {
+  $or(query: any[]): queryFilterCallback {
     const stack = this.parseQueryArray(query);
     const len = stack.length;
 
@@ -220,7 +228,7 @@ class QueryParser {
    * @return {queryFilterCallback}
    * @private
    */
-  $nor(query) {
+  $nor(query: any[]): queryFilterCallback {
     const stack = this.parseQueryArray(query);
     const len = stack.length;
 
@@ -238,7 +246,7 @@ class QueryParser {
    * @return {queryFilterCallback}
    * @private
    */
-  $not(query) {
+  $not(query: any): queryFilterCallback {
     const stack = this.parseQuery(query);
     const len = stack.length;
 
@@ -262,7 +270,7 @@ class QueryParser {
    * @return {queryFilterCallback}
    * @private
    */
-  $where(fn) {
+  $where(fn: (...args: any[]) => boolean): queryFilterCallback {
     return data => Reflect.apply(fn, data, []);
   }
 
@@ -273,7 +281,7 @@ class QueryParser {
    * @return {queryFilterCallback[]}
    * @private
    */
-  parseQueryArray(arr) {
+  parseQueryArray(arr: any[]): queryFilterCallback[] {
     const stack = [];
     this.$and(arr, stack);
     return stack;
@@ -288,7 +296,7 @@ class QueryParser {
    * @return {void}
    * @private
    */
-  parseNormalQuery(queries, prefix, stack = []) {
+  parseNormalQuery(queries: object, prefix: string, stack: queryFilterCallback[] = []): void {
     const keys = Object.keys(queries);
 
     for (let i = 0, len = keys.length; i < len; i++) {
@@ -316,10 +324,10 @@ class QueryParser {
    * @return {queryFilterCallback[]}
    * @private
    */
-  parseQuery(queries) {
+  parseQuery(queries: any): queryFilterCallback[] {
 
     /** @type {queryFilterCallback[]} */
-    const stack = [];
+    const stack: queryFilterCallback[] = [];
     const keys = Object.keys(queries);
 
     for (let i = 0, len = keys.length; i < len; i++) {
@@ -366,7 +374,7 @@ class QueryParser {
    * @return {queryFilterCallback}
    * @private
    */
-  execQuery(query) {
+  execQuery(query: object): queryFilterCallback {
     const stack = this.parseQuery(query);
     const len = stack.length;
 
@@ -392,7 +400,7 @@ class Schema {
    *
    * @param {Object} [schema]
    */
-  constructor(schema?) {
+  constructor(schema?: object) {
     this.hooks = {
       pre: {
         save: [],
@@ -422,7 +430,7 @@ class Schema {
    * @param {Object} schema
    * @param {String} prefix
    */
-  add(schema: Record<string, any>, prefix = ''): void {
+  add(schema: Record<string, any>, prefix: string = ''): void {
     const keys = Object.keys(schema);
     const len = keys.length;
 
@@ -458,7 +466,7 @@ class Schema {
     } else {
       switch (typeof obj) {
         case 'function':
-          type = getSchemaType(name, {type: obj});
+          type = getSchemaType(name, { type: obj });
           break;
 
         case 'object':
@@ -493,7 +501,7 @@ class Schema {
    * @param {SchemaType} type
    * @private
    */
-  _updateStack(name: string, type: SchemaType<unknown>) {
+  _updateStack(name: string, type: SchemaType<unknown>): void {
     const { stacks } = this;
 
     stacks.getter.push(data => {
@@ -559,7 +567,7 @@ class Schema {
    * @param {String} type Hook type. One of `save` or `remove`.
    * @param {Function} fn
    */
-  pre(type, fn) {
+  pre(type: string, fn: (callback: NodeJSLikeCallback<any, any>, options?: Promise.PromisifyOptions) => void): void {
     checkHookType(type);
     if (typeof fn !== 'function') throw new TypeError('Hook must be a function!');
 
@@ -572,7 +580,7 @@ class Schema {
    * @param {String} type Hook type. One of `save` or `remove`.
    * @param {Function} fn
    */
-  post(type, fn) {
+  post(type: string, fn: (callback: NodeJSLikeCallback<any, any>, options?: Promise.PromisifyOptions) => void): void {
     checkHookType(type);
     if (typeof fn !== 'function') throw new TypeError('Hook must be a function!');
 
@@ -585,7 +593,7 @@ class Schema {
    * @param {String} name
    * @param {Function} fn
    */
-  method(name, fn) {
+  method(name: string | number, fn: (...args: any[]) => any) {
     if (!name) throw new TypeError('Method name is required!');
 
     if (typeof fn !== 'function') {
@@ -601,7 +609,7 @@ class Schema {
    * @param {String} name
    * @param {Function} fn
    */
-  static(name: string, fn) {
+  static(name: string, fn: (...args: any[]) => any) {
     if (!name) throw new TypeError('Method name is required!');
 
     if (typeof fn !== 'function') {
@@ -618,7 +626,7 @@ class Schema {
    * @return {void}
    * @private
    */
-  _applyGetters(data) {
+  _applyGetters(data: object): void {
     const stack = this.stacks.getter;
 
     for (let i = 0, len = stack.length; i < len; i++) {
@@ -633,7 +641,7 @@ class Schema {
    * @return {void}
    * @private
    */
-  _applySetters(data) {
+  _applySetters(data: object): void {
     const stack = this.stacks.setter;
 
     for (let i = 0, len = stack.length; i < len; i++) {
@@ -682,7 +690,7 @@ class Schema {
    * @return {queryCallback[]}
    * @private
    */
-  _parseUpdate(updates) {
+  _parseUpdate(updates): queryCallback[] {
     return new UpdateParser(this.paths).parseUpdate(updates);
   }
 
@@ -693,7 +701,7 @@ class Schema {
    * @return {queryFilterCallback}
    * @private
    */
-  _execQuery(query) {
+  _execQuery(query): queryFilterCallback {
     return new QueryParser(this.paths).execQuery(query);
   }
 
@@ -707,7 +715,7 @@ class Schema {
    * @return {queryParseCallback[]}
    * @private
    */
-  _parseSort(sorts, prefix = '', stack = []) {
+  _parseSort(sorts: object, prefix: string = '', stack: queryParseCallback[] = []): queryParseCallback[] {
     const { paths } = this;
     const keys = Object.keys(sorts);
 
@@ -733,7 +741,7 @@ class Schema {
    * @return {queryParseCallback}
    * @private
    */
-  _execSort(sorts) {
+  _execSort(sorts: object): queryParseCallback {
     const stack = this._parseSort(sorts);
     return execSortStack(stack);
   }
@@ -746,7 +754,7 @@ class Schema {
    * @private
    */
   // eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
-  _parsePopulate(expr) {
+  _parsePopulate(expr: string | any[] | { path?: string; model?: any; [key: PropertyKey]: any }): PopulateResult[] {
     const { paths } = this;
     const arr = [];
 
diff --git a/src/schematype.ts b/src/schematype.ts
index 22dea735..5983af70 100644
--- a/src/schematype.ts
+++ b/src/schematype.ts
@@ -56,7 +56,7 @@ class SchemaType<T> {
    *   @param {Boolean} [options.required=false]
    *   @param {*} [options.default]
    */
-  constructor(public name = '', options?: { required?: boolean; default?: (() => T) | T; }) {
+  constructor(public name: string = '', options?: { required?: boolean; default?: (() => T) | T; }) {
     this.options = Object.assign({
       required: false
     }, options);
@@ -244,7 +244,7 @@ class SchemaType<T> {
    * @param {Object} data
    * @return {Boolean}
    */
-  q$nin(value, query, data?) {
+  q$nin(value: unknown, query: unknown[], data?: unknown): boolean {
     return !query.includes(value);
   }
 
@@ -256,7 +256,7 @@ class SchemaType<T> {
    * @param {Object} data
    * @return {*}
    */
-  u$set(value, update, data?) {
+  u$set<T>(value: unknown, update: T, data?: unknown): T {
     return update;
   }
 
@@ -268,7 +268,7 @@ class SchemaType<T> {
    * @param {Object} data
    * @return {*}
    */
-  u$unset(value, update, data?) { return update ? undefined : value; }
+  u$unset<T>(value: T, update: boolean, data?: unknown): T | undefined { return update ? undefined : value; }
 
   /**
    * Renames a field.
@@ -278,7 +278,7 @@ class SchemaType<T> {
    * @param {Object} data
    * @return {*}
    */
-  u$rename(value, update, data): void {
+  u$rename(value: unknown, update: unknown, data: unknown): void {
     if (value !== undefined) setProp(data, update, value);
     return undefined;
   }
diff --git a/src/types.ts b/src/types.ts
new file mode 100644
index 00000000..d7124870
--- /dev/null
+++ b/src/types.ts
@@ -0,0 +1,8 @@
+type NodeJSLikeCallback<R, E = any> = (err: E, result?: R) => void
+
+interface Options {
+  lean?: boolean;
+  skip?: number;
+  limit?: number;
+  [key: PropertyKey]: any;
+}
\ No newline at end of file
diff --git a/src/types/array.ts b/src/types/array.ts
index 3c51f36f..493dbce5 100644
--- a/src/types/array.ts
+++ b/src/types/array.ts
@@ -29,10 +29,12 @@ class SchemaTypeArray<I, T extends SchemaType<I>> extends SchemaType<I[]> {
   /**
    * Casts an array and its child elements.
    *
-   * @param {*} value
+   * @param {*} value_
    * @param {Object} data
    * @return {Array}
    */
+  cast(value_: Exclude<unknown, null | undefined>, data?: unknown): I[];
+  cast(value_?: unknown, data?: unknown): I[] | null | undefined;
   cast(value_?: unknown, data?: unknown): I[] | null | undefined {
     value_ = super.cast(value_, data);
     if (value_ == null) return value_ as null | undefined;
@@ -52,7 +54,7 @@ class SchemaTypeArray<I, T extends SchemaType<I>> extends SchemaType<I[]> {
   /**
    * Validates an array and its child elements.
    *
-   * @param {*} value
+   * @param {*} value_
    * @param {Object} data
    * @return {Array|Error}
    */
@@ -107,8 +109,10 @@ class SchemaTypeArray<I, T extends SchemaType<I>> extends SchemaType<I[]> {
    * @param {Array} value
    * @return {Array}
    */
-  parse(value?: unknown[]) {
-    if (!value) return value;
+  parse(value: unknown[]): I[];
+  parse(): undefined;
+  parse(value?: unknown[]): I[] | undefined {
+    if (!value) return value as undefined;
 
     const len = value.length;
     if (!len) return [];
@@ -117,7 +121,7 @@ class SchemaTypeArray<I, T extends SchemaType<I>> extends SchemaType<I[]> {
     const child = this.child;
 
     for (let i = 0; i < len; i++) {
-      result[i] = child.parse(value[i]);
+      result[i] = child.parse(value[i]) as I;
     }
 
     return result;
@@ -130,8 +134,10 @@ class SchemaTypeArray<I, T extends SchemaType<I>> extends SchemaType<I[]> {
    * @param {Object} data
    * @return {Array}
    */
-  value(value?: unknown[], data?: unknown): any[] {
-    if (!value) return value;
+  value(value: unknown[], data?: unknown): any[]
+  value(): undefined;
+  value(value?: unknown[], data?: unknown): any[] | undefined {
+    if (!value) return value as undefined;
 
     const len = value.length;
     if (!len) return [];
@@ -211,7 +217,7 @@ class SchemaTypeArray<I, T extends SchemaType<I>> extends SchemaType<I[]> {
    * @param {Object} data
    * @return {Boolean}
    */
-  q$nin(value?: unknown[], query?: unknown[], data?: unknown): boolean {
+  q$nin<T>(value?: T[], query?: T[], data?: unknown): boolean {
     if (!value) return true;
 
     for (let i = 0, len = query.length; i < len; i++) {
@@ -229,7 +235,7 @@ class SchemaTypeArray<I, T extends SchemaType<I>> extends SchemaType<I[]> {
    * @param {Object} data
    * @return {Boolean}
    */
-  q$all(value?: unknown[], query?: unknown[], data?: unknown): boolean {
+  q$all<T>(value?: T[], query?: T[], data?: unknown): boolean {
     if (!value) return false;
 
     for (let i = 0, len = query.length; i < len; i++) {
@@ -268,7 +274,7 @@ class SchemaTypeArray<I, T extends SchemaType<I>> extends SchemaType<I[]> {
    * @param {Object} data
    * @return {Array}
    */
-  u$unshift(value?: unknown[], update?: unknown, data?: unknown): any[] {
+  u$unshift<T>(value?: T[], update?: T | T[], data?: unknown): T[] {
     if (isArray(update)) {
       return value ? update.concat(value) : update;
     }
@@ -289,7 +295,7 @@ class SchemaTypeArray<I, T extends SchemaType<I>> extends SchemaType<I[]> {
    * @param {Object} data
    * @return {Array}
    */
-  u$pull(value?: unknown[], update?: unknown, data?: unknown): any[] {
+  u$pull<T>(value?: T[], update?: T | T[], data?: unknown): T[] {
     if (!value) return value;
 
     if (isArray(update)) {
@@ -307,7 +313,7 @@ class SchemaTypeArray<I, T extends SchemaType<I>> extends SchemaType<I[]> {
    * @param {Object} data
    * @return {Array}
    */
-  u$shift(value?, update?, data?) {
+  u$shift<T>(value?: T[], update?: number | boolean, data?: unknown): T[] {
     if (!value || !update) return value;
 
     if (update === true) {
@@ -327,7 +333,7 @@ class SchemaTypeArray<I, T extends SchemaType<I>> extends SchemaType<I[]> {
    * @param {Object} data
    * @return {Array}
    */
-  u$pop(value?, update?, data?) {
+  u$pop<T>(value?: T[], update?: number | boolean, data?: unknown): T[] {
     if (!value || !update) return value;
 
     const length = value.length;
@@ -349,7 +355,7 @@ class SchemaTypeArray<I, T extends SchemaType<I>> extends SchemaType<I[]> {
    * @param {Object} data
    * @return {Array}
    */
-  u$addToSet(value?: any[], update?, data?) {
+  u$addToSet<T>(value?: T[], update?: T | T[], data?: unknown): T[] {
     if (isArray(update)) {
       if (!value) return update;
 
diff --git a/src/types/boolean.ts b/src/types/boolean.ts
index 55330fde..1160dfe2 100644
--- a/src/types/boolean.ts
+++ b/src/types/boolean.ts
@@ -9,7 +9,7 @@ class SchemaTypeBoolean extends SchemaType<boolean> {
   /**
    * Casts a boolean.
    *
-   * @param {*} value
+   * @param {*} value_
    * @param {Object} data
    * @return {Boolean}
    */
@@ -24,7 +24,7 @@ class SchemaTypeBoolean extends SchemaType<boolean> {
   /**
    * Validates a boolean.
    *
-   * @param {*} value
+   * @param {*} value_
    * @param {Object} data
    * @return {Boolean|Error}
    */
diff --git a/src/types/buffer.ts b/src/types/buffer.ts
index 73cc157e..7cb1da73 100644
--- a/src/types/buffer.ts
+++ b/src/types/buffer.ts
@@ -14,7 +14,7 @@ class SchemaTypeBuffer extends SchemaType<Buffer> {
    *   @param {boolean|Function} [options.default]
    *   @param {string} [options.encoding=hex]
    */
-  constructor(name: string, options?) {
+  constructor(name: string, options?: Partial<SchemaType<Buffer>['options']> & { encoding?: BufferEncoding; }) {
     super(name, Object.assign({
       encoding: 'hex'
     }, options));
@@ -23,11 +23,13 @@ class SchemaTypeBuffer extends SchemaType<Buffer> {
   /**
    * Casts data.
    *
-   * @param {*} value
+   * @param {*} value_
    * @param {Object} data
    * @return {Buffer}
    */
-  cast(value_?: unknown, data?): Buffer | null | undefined {
+  cast(value_: WithImplicitCoercion<Uint8Array | ReadonlyArray<number> | string>, data?: unknown): Buffer;
+  cast(value_?: unknown, data?: unknown): Buffer | null | undefined;
+  cast(value_?: unknown, data?: unknown): Buffer | null | undefined {
     const value = super.cast(value_, data);
 
     if (value == null || Buffer.isBuffer(value)) return value as Buffer | null | undefined;
@@ -38,11 +40,11 @@ class SchemaTypeBuffer extends SchemaType<Buffer> {
   /**
    * Validates data.
    *
-   * @param {*} value
+   * @param {*} value_
    * @param {Object} data
    * @return {Buffer}
    */
-  validate(value_: unknown, data?): Buffer {
+  validate(value_: unknown, data?: unknown): Buffer {
     const value = super.validate(value_, data);
 
     if (!Buffer.isBuffer(value)) {
@@ -73,7 +75,9 @@ class SchemaTypeBuffer extends SchemaType<Buffer> {
    * @param {*} value
    * @return {Boolean}
    */
-  parse(value?) {
+  parse(value: WithImplicitCoercion<Uint8Array | ReadonlyArray<number> | string>): Buffer;
+  parse(value?: unknown): Buffer | null | undefined;
+  parse(value?: any): Buffer | null | undefined {
     return value ? Buffer.from(value, this.options.encoding) : value;
   }
 
@@ -81,9 +85,9 @@ class SchemaTypeBuffer extends SchemaType<Buffer> {
    * Transforms data into number to compress the size of database files.
    *
    * @param {Buffer} value
-   * @return {Number}
+   * @return {String}
    */
-  value(value?: Buffer) {
+  value(value?: Buffer): string {
     return Buffer.isBuffer(value) ? value.toString(this.options.encoding) : value;
   }
 
diff --git a/src/types/cuid.ts b/src/types/cuid.ts
index 49b057c6..476cfa0c 100644
--- a/src/types/cuid.ts
+++ b/src/types/cuid.ts
@@ -14,7 +14,7 @@ class SchemaTypeCUID extends SchemaType<string> {
    * @param {String} value
    * @return {String}
    */
-  cast(value?) {
+  cast(value?: string): string {
     if (value == null && this.options.required) {
       return cuid();
     }
@@ -28,7 +28,7 @@ class SchemaTypeCUID extends SchemaType<string> {
    * @param {*} value
    * @return {String|Error}
    */
-  validate(value?) {
+  validate(value?: string): string {
     if (value && (value[0] !== 'c' || value.length !== 25)) {
       throw new ValidationError(`\`${value}\` is not a valid CUID`);
     }
diff --git a/src/types/date.ts b/src/types/date.ts
index 40727b87..636e29be 100644
--- a/src/types/date.ts
+++ b/src/types/date.ts
@@ -9,14 +9,12 @@ class SchemaTypeDate extends SchemaType<Date> {
   /**
    * Casts data.
    *
-   * @param {*} value
+   * @param {*} value_
    * @return {Date | null | undefined}
    */
-  cast(value_?): Date | null | undefined;
-  cast(value_: Date): Date;
-  cast(value_: null): Date | null;
-  cast(value_: undefined): Date | undefined;
-  cast(value_: unknown): Date | null | undefined {
+  cast(value_: Date | number | string): Date;
+  cast(value_?: unknown): Date | null | undefined;
+  cast(value_?: unknown): Date | null | undefined {
     const value = super.cast(value_, null);
 
     if (value == null || value instanceof Date) return value as Date | null | undefined;
@@ -27,18 +25,18 @@ class SchemaTypeDate extends SchemaType<Date> {
   /**
    * Validates data.
    *
-   * @param {*} value
+   * @param {*} value_
    * @param {Object} data
    * @return {Date|Error}
    */
-  validate(value_, data?) {
+  validate(value_: unknown, data?: unknown): Date {
     const value = super.validate(value_, data);
 
     if (value != null && (!(value instanceof Date) || isNaN(value.getTime()))) {
       throw new ValidationError(`\`${value}\` is not a valid date!`);
     }
 
-    return value;
+    return value as Date;
   }
 
   /**
@@ -63,9 +61,9 @@ class SchemaTypeDate extends SchemaType<Date> {
    * @param {Date} b
    * @return {Number}
    */
-  compare(a?, b?) {
+  compare(a?: Date, b?: Date): number {
     if (a) {
-      return b ? a - b : 1;
+      return b ? (a as unknown as number) - (b as unknown as number) : 1;
     }
 
     return b ? -1 : 0;
@@ -77,7 +75,9 @@ class SchemaTypeDate extends SchemaType<Date> {
    * @param {*} value
    * @return {Date}
    */
-  parse(value?) {
+  parse(value: string | number | Date): Date;
+  parse(): undefined;
+  parse(value?: string | number | Date): Date | undefined {
     if (value) return new Date(value);
   }
 
@@ -87,8 +87,10 @@ class SchemaTypeDate extends SchemaType<Date> {
    * @param {Date} value
    * @return {String}
    */
-  value(value?) {
-    return value ? value.toISOString() : value;
+  value(value: Date): string;
+  value(): undefined;
+  value(value?: Date): string | undefined {
+    return value ? value.toISOString() : value as undefined;
   }
 
   /**
@@ -98,7 +100,7 @@ class SchemaTypeDate extends SchemaType<Date> {
    * @param {Number} query
    * @return {Boolean}
    */
-  q$day(value, query) {
+  q$day(value: Date | undefined, query: number): boolean {
     return value ? value.getDate() === query : false;
   }
 
@@ -109,7 +111,7 @@ class SchemaTypeDate extends SchemaType<Date> {
    * @param {Number} query
    * @return {Boolean}
    */
-  q$month(value, query) {
+  q$month(value: Date | undefined, query: number): boolean {
     return value ? value.getMonth() === query : false;
   }
 
@@ -120,7 +122,7 @@ class SchemaTypeDate extends SchemaType<Date> {
    * @param {Number} query
    * @return {Boolean}
    */
-  q$year(value, query) {
+  q$year(value: Date | undefined, query: number): boolean {
     return value ? value.getFullYear() === query : false;
   }
 
@@ -131,7 +133,7 @@ class SchemaTypeDate extends SchemaType<Date> {
    * @param {Number} update
    * @return {Date}
    */
-  u$inc(value, update) {
+  u$inc(value: Date | undefined, update: number): Date {
     if (value) return new Date(value.getTime() + update);
   }
 
@@ -142,7 +144,7 @@ class SchemaTypeDate extends SchemaType<Date> {
    * @param {Number} update
    * @return {Date}
    */
-  u$dec(value, update) {
+  u$dec(value: Date | undefined, update: number): Date {
     if (value) return new Date(value.getTime() - update);
   }
 }
diff --git a/src/types/enum.ts b/src/types/enum.ts
index 1a96d88c..42ee6c26 100644
--- a/src/types/enum.ts
+++ b/src/types/enum.ts
@@ -15,7 +15,7 @@ class SchemaTypeEnum extends SchemaType<any[]> {
    *   @param {Array} options.elements
    *   @param {*} [options.default]
    */
-  constructor(name, options) {
+  constructor(name: string, options?: Partial<SchemaType<any[]>['options']> & { elements?: any[] }) {
     super(name, Object.assign({
       elements: []
     }, options));
@@ -24,11 +24,11 @@ class SchemaTypeEnum extends SchemaType<any[]> {
   /**
    * Validates data. The value must be one of elements set in the options.
    *
-   * @param {*} value
+   * @param {*} value_
    * @param {Object} data
    * @return {*}
    */
-  validate(value_, data?) {
+  validate(value_: unknown, data?: unknown) {
     const value = super.validate(value_, data);
     const elements = this.options.elements;
 
diff --git a/src/types/integer.ts b/src/types/integer.ts
index 97b74d5e..c5400212 100644
--- a/src/types/integer.ts
+++ b/src/types/integer.ts
@@ -9,11 +9,11 @@ class SchemaTypeInteger extends SchemaTypeNumber {
   /**
    * Casts a integer.
    *
-   * @param {*} value
+   * @param {*} value_
    * @param {Object} data
    * @return {Number}
    */
-  cast(value_?, data?): number {
+  cast(value_?: unknown, data?: unknown): number {
     const value = super.cast(value_, data);
 
     return parseInt(value as any, 10);
@@ -22,11 +22,11 @@ class SchemaTypeInteger extends SchemaTypeNumber {
   /**
    * Validates an integer.
    *
-   * @param {*} value
+   * @param {*} value_
    * @param {Object} data
    * @return {Number|Error}
    */
-  validate(value_?, data?): number {
+  validate(value_?: unknown, data?: unknown): number {
     const value = super.validate(value_, data);
 
     if (!Number.isInteger(value)) {
diff --git a/src/types/number.ts b/src/types/number.ts
index 83dcbe2c..fdae9c87 100644
--- a/src/types/number.ts
+++ b/src/types/number.ts
@@ -13,7 +13,9 @@ class SchemaTypeNumber extends SchemaType<number> {
    * @param {Object} data
    * @return {Number}
    */
-  cast(value_?, data?): number | null | undefined {
+  cast(value_: Exclude<unknown, undefined | null>, data?: unknown): number;
+  cast(value_?: unknown, data?: unknown): number | null | undefined;
+  cast(value_?: unknown, data?: unknown): number | null | undefined {
     const value = super.cast(value_, data);
 
     if (value == null || typeof value === 'number') return value as number | null | undefined;
@@ -28,14 +30,14 @@ class SchemaTypeNumber extends SchemaType<number> {
    * @param {Object} data
    * @return {Number|Error}
    */
-  validate(value_?, data?) {
+  validate(value_?: unknown, data?: unknown): number {
     const value = super.validate(value_, data);
 
     if (value !== undefined && (typeof value !== 'number' || isNaN(value))) {
       throw new ValidationError(`\`${value}\` is not a number!`);
     }
 
-    return value;
+    return value as number;
   }
 
   /**
@@ -45,7 +47,7 @@ class SchemaTypeNumber extends SchemaType<number> {
    * @param {Number} update
    * @return {Number}
    */
-  u$inc(value, update) {
+  u$inc(value: number | undefined, update: number): number {
     return value ? value + update : update;
   }
 
@@ -56,7 +58,7 @@ class SchemaTypeNumber extends SchemaType<number> {
    * @param {Number} update
    * @return {Number}
    */
-  u$dec(value, update) {
+  u$dec(value: number | undefined, update: number): number {
     return value ? value - update : -update;
   }
 
@@ -67,7 +69,7 @@ class SchemaTypeNumber extends SchemaType<number> {
    * @param {Number} update
    * @return {Number}
    */
-  u$mul(value, update) {
+  u$mul(value: number | undefined, update: number): number {
     return value ? value * update : 0;
   }
 
@@ -78,7 +80,7 @@ class SchemaTypeNumber extends SchemaType<number> {
    * @param {Number} update
    * @return {Number}
    */
-  u$div(value, update) {
+  u$div(value: number | undefined, update: number): number {
     return value ? value / update : 0;
   }
 
@@ -89,7 +91,7 @@ class SchemaTypeNumber extends SchemaType<number> {
    * @param {Number} update
    * @return {Number}
    */
-  u$mod(value, update) {
+  u$mod(value: number | undefined, update: number): number {
     return value ? value % update : 0;
   }
 
@@ -100,7 +102,7 @@ class SchemaTypeNumber extends SchemaType<number> {
    * @param {Number} update
    * @return {Number}
    */
-  u$max(value, update) {
+  u$max(value: number | undefined, update: number): number {
     return update > value ? update : value;
   }
 
@@ -111,7 +113,7 @@ class SchemaTypeNumber extends SchemaType<number> {
    * @param {Number} update
    * @return {Number}
    */
-  u$min(value, update) {
+  u$min(value: number | undefined, update: number): number {
     return update < value ? update : value;
   }
 }
diff --git a/src/types/object.ts b/src/types/object.ts
index 840fa20c..7024288d 100644
--- a/src/types/object.ts
+++ b/src/types/object.ts
@@ -12,7 +12,7 @@ class SchemaTypeObject extends SchemaType<Record<string, any>> {
    *   @param {Boolean} [options.required=false]
    *   @param {Object|Function} [options.default={}]
    */
-  constructor(name?, options?) {
+  constructor(name?: string, options?: Partial<SchemaType<Record<string, any>>['options']>) {
     super(name, Object.assign({ default: {} }, options));
   }
 }
diff --git a/src/types/string.ts b/src/types/string.ts
index 589ee085..1156078e 100644
--- a/src/types/string.ts
+++ b/src/types/string.ts
@@ -9,32 +9,34 @@ class SchemaTypeString extends SchemaType<string> {
   /**
    * Casts a string.
    *
-   * @param {*} value
+   * @param {*} value_
    * @param {Object} data
    * @return {String}
    */
-  cast(value_?, data?) {
+  cast(value_: { toString(): string }, data?: unknown): string;
+  cast(value_?: unknown, data?: unknown): string | null | undefined;
+  cast(value_?: unknown, data?: unknown): string | null | undefined {
     const value = super.cast(value_, data);
 
-    if (value == null || typeof value === 'string') return value;
+    if (value == null || typeof value === 'string') return value as string | null | undefined;
     if (typeof value.toString === 'function') return value.toString();
   }
 
   /**
    * Validates a string.
    *
-   * @param {*} value
+   * @param {*} value_
    * @param {Object} data
    * @return {String|Error}
    */
-  validate(value_?, data?) {
+  validate(value_?: unknown, data?: unknown): string {
     const value = super.validate(value_, data);
 
     if (value !== undefined && typeof value !== 'string') {
       throw new ValidationError(`\`${value}\` is not a string!`);
     }
 
-    return value;
+    return value as string;
   }
 
   /**
@@ -45,13 +47,13 @@ class SchemaTypeString extends SchemaType<string> {
    * @param {Object} data
    * @return {Boolean}
    */
-  match(value, query, data?) {
+  match(value: string | undefined, query: string | RegExp | undefined, data?: unknown): boolean {
     if (!value || !query) {
       return value === query;
     }
 
-    if (typeof query.test === 'function') {
-      return query.test(value);
+    if (typeof (query as any).test === 'function') {
+      return (query as RegExp).test(value);
     }
 
     return value === query;
@@ -65,7 +67,7 @@ class SchemaTypeString extends SchemaType<string> {
    * @param {Object} data
    * @return {Boolean}
    */
-  q$in(value, query, data?) {
+  q$in(value: string | undefined, query: string[] | RegExp[], data?: unknown): boolean {
     for (let i = 0, len = query.length; i < len; i++) {
       if (this.match(value, query[i], data)) return true;
     }
@@ -81,7 +83,7 @@ class SchemaTypeString extends SchemaType<string> {
    * @param {Object} data
    * @return {Boolean}
    */
-  q$nin(value, query, data?) {
+  q$nin(value: string | undefined, query: string[] | RegExp[], data?: unknown): boolean {
     return !this.q$in(value, query, data);
   }
 
@@ -92,7 +94,7 @@ class SchemaTypeString extends SchemaType<string> {
    * @param {Number} query
    * @return {Boolean}
    */
-  q$length(value, query) {
+  q$length(value: string | undefined, query: number): boolean {
     return (value ? value.length : 0) === query;
   }
 }
diff --git a/src/types/virtual.ts b/src/types/virtual.ts
index aa333a5a..383907b3 100644
--- a/src/types/virtual.ts
+++ b/src/types/virtual.ts
@@ -14,7 +14,7 @@ class SchemaTypeVirtual extends SchemaType<any> {
    * @param {Function} fn
    * @chainable
    */
-  get(fn) {
+  get(fn: () => any): SchemaTypeVirtual {
     if (typeof fn !== 'function') {
       throw new TypeError('Getter must be a function!');
     }
@@ -30,7 +30,7 @@ class SchemaTypeVirtual extends SchemaType<any> {
    * @param {Function} fn
    * @chainable
    */
-  set(fn) {
+  set(fn: (value: any) => void): SchemaTypeVirtual {
     if (typeof fn !== 'function') {
       throw new TypeError('Setter must be a function!');
     }
@@ -47,7 +47,7 @@ class SchemaTypeVirtual extends SchemaType<any> {
    * @param {Object} data
    * @return {*}
    */
-  cast(value, data) {
+  cast(value: unknown, data: any): void {
     if (typeof this.getter !== 'function') return;
 
     const getter = this.getter;
@@ -70,7 +70,7 @@ class SchemaTypeVirtual extends SchemaType<any> {
    * @param {*} value
    * @param {Object} data
    */
-  validate(value, data) {
+  validate(value: any, data: any): void {
     if (typeof this.setter === 'function') {
       this.setter.call(data, value);
     }
diff --git a/src/util.ts b/src/util.ts
index 62cef092..b7ab5d57 100644
--- a/src/util.ts
+++ b/src/util.ts
@@ -1,8 +1,8 @@
-function extractPropKey(key) {
+function extractPropKey(key: string): string[] {
   return key.split('.');
 }
 
-function _parseArgs(args) {
+function _parseArgs(args: string) {
   if (typeof args !== 'string') return args;
 
   const arr = args.split(' ');
@@ -173,12 +173,12 @@ export function reverse(arr) {
   return arr;
 }
 
-export function parseArgs(orderby, order?) {
+export function parseArgs(orderby: string | object, order?: string | number | object) {
   let result;
 
   if (order) {
     result = {};
-    result[orderby] = order;
+    result[orderby as string] = order;
   } else if (typeof orderby === 'string') {
     result = _parseArgs(orderby);
   } else {
diff --git a/test/scripts/document.ts b/test/scripts/document.ts
index abac13a4..3d92fd35 100644
--- a/test/scripts/document.ts
+++ b/test/scripts/document.ts
@@ -39,7 +39,7 @@ describe('Document', () => {
     const doc = User.new({});
 
     return doc.save().then(item => {
-      User.findById(doc._id).should.exist;
+      User.findById(doc._id as string | number).should.exist;
       return User.removeById(item._id);
     });
   });
@@ -115,5 +115,5 @@ describe('Document', () => {
 
     user.populate('comments').comments.toArray().should.eql(comments);
     return comments;
-  }).map(comment => Comment.removeById(comment._id)));
+  }).map<unknown, any>(comment => Comment.removeById(comment._id)));
 });
diff --git a/test/scripts/model.ts b/test/scripts/model.ts
index 88589338..f258031d 100644
--- a/test/scripts/model.ts
+++ b/test/scripts/model.ts
@@ -9,6 +9,8 @@ import Promise from 'bluebird';
 import sinon from 'sinon';
 import cuid from 'cuid';
 import Database from '../../dist/database';
+import type Query from '../../dist/query';
+import type Document from '../../dist/document';
 
 describe('Model', () => {
 
@@ -48,7 +50,7 @@ describe('Model', () => {
       age: 20
     });
 
-    user._id.should.exist;
+    user._id!.should.exist;
     user.name.first.should.eql('John');
     user.name.last.should.eql('Doe');
     user.name.full.should.eql('John Doe');
@@ -98,16 +100,16 @@ describe('Model', () => {
     const doc = User.new();
     delete doc._id;
 
-    return User.insert(doc).should.eventually.be.rejected;
+    return (User.insert(doc) as any).should.eventually.be.rejected;
   });
 
   it('insert() - already existed', () => {
     let user;
 
-    return User.insert({}).then(data => {
+    return (User.insert({}).then(data => {
       user = data;
       return User.insert(data);
-    }).finally(() => User.removeById(user._id)).should.eventually.be.rejected;
+    }).finally(() => User.removeById(user._id)) as any).should.eventually.be.rejected;
   });
 
   it('insert() - hook', () => {
@@ -150,7 +152,7 @@ describe('Model', () => {
   ]).then(data => {
     data.length = 2;
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('insert() - sync problem', () => {
     const db = new Database();
@@ -301,7 +303,7 @@ describe('Model', () => {
     return data;
   }).then(data => User.removeById(data._id)));
 
-  it('updateById() - id not exist', () => User.updateById('foo', {}).should.eventually.be.rejected);
+  it('updateById() - id not exist', () => (User.updateById('foo', {}) as any).should.eventually.be.rejected);
 
   it('updateById() - hook', () => {
     const db = new Database();
@@ -341,7 +343,7 @@ describe('Model', () => {
     updated[0].email.should.eql('A');
     updated[1].email.should.eql('A');
     return data;
-  })).map(item => User.removeById(item._id)));
+  })).map<unknown, any>(item => User.removeById(item._id)));
 
   it('replaceById()', () => {
     function validate(data) {
@@ -371,7 +373,7 @@ describe('Model', () => {
     }).then(data => User.removeById(data._id));
   });
 
-  it('replaceById() - id not exist', () => User.replaceById('foo', {}).should.eventually.be.rejected);
+  it('replaceById() - id not exist', () => (User.replaceById('foo', {}) as any).should.eventually.be.rejected);
 
   it('replaceById() - pre-hook', () => {
     const db = new Database();
@@ -411,7 +413,7 @@ describe('Model', () => {
     updated[0].email.should.eql('A');
     updated[1].email.should.eql('A');
     return data;
-  })).map(item => User.removeById(item._id)));
+  })).map<unknown, any>(item => User.removeById(item._id)));
 
   it('removeById()', () => {
     const listener = sinon.spy(data => {
@@ -430,7 +432,7 @@ describe('Model', () => {
     });
   });
 
-  it('removeById() - id not exist', () => User.removeById('foo', {}).should.eventually.be.rejected);
+  it('removeById() - id not exist', () => (User.removeById('foo', {}) as any).should.eventually.be.rejected);
 
   it('removeById() - hook', () => {
     const db = new Database();
@@ -489,13 +491,13 @@ describe('Model', () => {
 
       count.should.eql(data.length);
       return data;
-    }).map(item => Post.removeById(item._id));
+    }).map<unknown, any>(item => Post.removeById(item._id));
   });
 
   it('toArray()', () => Post.insert(Array(10).fill({})).then(data => {
     Post.toArray().should.eql(data);
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('find()', () => User.insert([
     {age: 10},
@@ -504,10 +506,10 @@ describe('Model', () => {
     {age: 30},
     {age: 40}
   ]).then(data => {
-    const query = User.find({age: 20});
+    const query = User.find({age: 20}) as Query;
     query.data.should.eql(data.slice(1, 3));
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - blank', () => User.insert([
     {age: 10},
@@ -516,10 +518,10 @@ describe('Model', () => {
     {age: 30},
     {age: 40}
   ]).then(data => {
-    const query = User.find({});
+    const query = User.find({}) as Query;
     query.data.should.eql(data);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - operator', () => User.insert([
     {age: 10},
@@ -527,10 +529,10 @@ describe('Model', () => {
     {age: 30},
     {age: 40}
   ]).then(data => {
-    const query = User.find({age: {$gt: 20}});
+    const query = User.find({age: {$gt: 20}}) as Query;
     query.data.should.eql(data.slice(2));
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - limit', () => User.insert([
     {age: 10},
@@ -538,10 +540,10 @@ describe('Model', () => {
     {age: 30},
     {age: 40}
   ]).then(data => {
-    const query = User.find({age: {$gte: 20}}, {limit: 2});
+    const query = User.find({age: {$gte: 20}}, {limit: 2}) as Query;
     query.data.should.eql(data.slice(1, 3));
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - skip', () => User.insert([
     {age: 10},
@@ -549,15 +551,15 @@ describe('Model', () => {
     {age: 30},
     {age: 40}
   ]).then(data => {
-    let query = User.find({age: {$gte: 20}}, {skip: 1});
+    let query = User.find({age: {$gte: 20}}, {skip: 1}) as Query;
     query.data.should.eql(data.slice(2));
 
     // with limit
-    query = User.find({age: {$gte: 20}}, {limit: 1, skip: 1});
+    query = User.find({age: {$gte: 20}}, {limit: 1, skip: 1}) as Query;
     query.data.should.eql(data.slice(2, 3));
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - lean', () => User.insert([
     {age: 10},
@@ -568,7 +570,7 @@ describe('Model', () => {
     const query = User.find({age: {$gt: 20}}, {lean: true});
     query.should.be.a('array');
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - $and', () => User.insert([
     {name: {first: 'John', last: 'Doe'}, age: 20},
@@ -582,10 +584,10 @@ describe('Model', () => {
       ]
     });
 
-    query.toArray().should.eql([data[1]]);
+    (query as Query).toArray().should.eql([data[1]]);
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - $or', () => User.insert([
     {name: {first: 'John', last: 'Doe'}, age: 20},
@@ -599,10 +601,10 @@ describe('Model', () => {
       ]
     });
 
-    query.toArray().should.eql(data.slice(1));
+    (query as Query).toArray().should.eql(data.slice(1));
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - $nor', () => User.insert([
     {name: {first: 'John', last: 'Doe'}, age: 20},
@@ -616,10 +618,10 @@ describe('Model', () => {
       ]
     });
 
-    query.toArray().should.eql([data[0]]);
+    (query as Query).toArray().should.eql([data[0]]);
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - $not', () => User.insert([
     {name: {first: 'John', last: 'Doe'}, age: 20},
@@ -630,10 +632,10 @@ describe('Model', () => {
       $not: {'name.last': 'Doe'}
     });
 
-    query.toArray().should.eql(data.slice(2));
+    (query as Query).toArray().should.eql(data.slice(2));
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - $where', () => User.insert([
     {name: {first: 'John', last: 'Doe'}, age: 20},
@@ -646,10 +648,10 @@ describe('Model', () => {
       }
     });
 
-    query.toArray().should.eql(data.slice(0, 2));
+    (query as Query).toArray().should.eql(data.slice(0, 2));
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('findOne()', () => User.insert([
     {age: 10},
@@ -659,7 +661,7 @@ describe('Model', () => {
   ]).then(data => {
     User.findOne({age: {$gt: 20}}).should.eql(data[2]);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('findOne() - lean', () => User.insert([
     {age: 10},
@@ -667,9 +669,9 @@ describe('Model', () => {
     {age: 30},
     {age: 40}
   ]).then(data => {
-    User.findOne({age: {$gt: 20}}, {lean: true})._id.should.eql(data[2]._id);
+    (User.findOne({age: {$gt: 20}}, {lean: true}) as Document)._id!.should.eql(data[2]._id);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('sort()', () => User.insert([
     {age: 15},
@@ -681,7 +683,7 @@ describe('Model', () => {
     query.data[1].should.eql(data[0]);
     query.data[2].should.eql(data[1]);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('sort() - descending', () => User.insert([
     {age: 15},
@@ -693,7 +695,7 @@ describe('Model', () => {
     query.data[1].should.eql(data[0]);
     query.data[2].should.eql(data[2]);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('sort() - multi', () => User.insert([
     {age: 15, email: 'A'},
@@ -707,7 +709,7 @@ describe('Model', () => {
     query.data[2].should.eql(data[3]);
     query.data[3].should.eql(data[1]);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('eq()', () => Post.insert(Array(5).fill({})).then(data => {
     for (let i = 0, len = data.length; i < len; i++) {
@@ -715,7 +717,7 @@ describe('Model', () => {
     }
 
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('eq() - negative index', () => Post.insert(Array(5).fill({})).then(data => {
     for (let i = 1, len = data.length; i <= len; i++) {
@@ -723,7 +725,7 @@ describe('Model', () => {
     }
 
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('eq() - no data', () => {
     (typeof Post.eq(1)).should.eql('undefined');
@@ -733,68 +735,68 @@ describe('Model', () => {
     Post.first().should.eql(data[0]);
 
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('last()', () => Post.insert(Array(5).fill({})).then(data => {
     Post.last().should.eql(data[data.length - 1]);
 
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('slice() - no arguments', () => Post.insert(Array(5).fill({})).then(data => {
     Post.slice().data.should.eql(data);
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('slice() - one argument', () => Post.insert(Array(5).fill({})).then(data => {
     Post.slice(2).data.should.eql(data.slice(2));
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('slice() - one negative argument', () => Post.insert(Array(5).fill({})).then(data => {
     Post.slice(-2).data.should.eql(data.slice(-2));
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('slice() - two arguments', () => Post.insert(Array(5).fill({})).then(data => {
     Post.slice(2, 4).data.should.eql(data.slice(2, 4));
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('slice() - start + negative end index', () => Post.insert(Array(5).fill({})).then(data => {
     Post.slice(1, -1).data.should.eql(data.slice(1, -1));
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('slice() - two negative arguments', () => Post.insert(Array(5).fill({})).then(data => {
     Post.slice(-3, -1).data.should.eql(data.slice(-3, -1));
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('slice() - start > end', () => Post.insert(Array(5).fill({})).then(data => {
     Post.slice(-1, -3).data.should.eql(data.slice(-1, -3));
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('slice() - index overflow', () => Post.insert(Array(5).fill({})).then(data => {
     Post.slice(1, 100).data.should.eql(data.slice(1, 100));
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('slice() - index overflow 2', () => Post.insert(Array(5).fill({})).then(data => {
     Post.slice(100, 200).data.should.eql(data.slice(100, 200));
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('limit()', () => Post.insert(Array(5).fill({})).then(data => {
     Post.limit(2).data.should.eql(data.slice(0, 2));
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('skip()', () => Post.insert(Array(5).fill({})).then(data => {
     Post.skip(2).data.should.eql(data.slice(2));
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('reverse()', () => Post.insert(Array(5).fill({})).then(data => {
     const query = Post.reverse();
@@ -804,13 +806,13 @@ describe('Model', () => {
     }
 
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('shuffle()', () => Post.insert(Array(5).fill({})).then(data => {
     const query = Post.shuffle();
     sortBy(query.data, '_id').should.eql(sortBy(data, '_id'));
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('map()', () => Post.insert(Array(5).fill({})).then(data => {
     let num = 0;
@@ -825,7 +827,7 @@ describe('Model', () => {
     d1.should.eql(d2);
 
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('reduce()', () => Post.insert([
     {email: 'A'},
@@ -842,7 +844,7 @@ describe('Model', () => {
     sum.email.should.eql('ABC');
 
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('reduce() - with initial', () => Post.insert([
     {email: 'A'},
@@ -859,7 +861,7 @@ describe('Model', () => {
     sum.should.eql('_ABC');
 
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('reduceRight()', () => Post.insert([
     {email: 'A'},
@@ -876,7 +878,7 @@ describe('Model', () => {
     sum.email.should.eql('CBA');
 
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('reduceRight() - with initial', () => Post.insert([
     {email: 'A'},
@@ -893,7 +895,7 @@ describe('Model', () => {
     sum.should.eql('_CBA');
 
     return data;
-  }).map(item => Post.removeById(item._id)));
+  }).map<unknown, any>(item => Post.removeById(item._id)));
 
   it('filter()', () => User.insert([
     {age: 10},
@@ -911,7 +913,7 @@ describe('Model', () => {
     query.data.should.eql(data.slice(2));
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('every()', () => User.insert([
     {age: 10},
@@ -929,7 +931,7 @@ describe('Model', () => {
     User.every((data, i) => data.age > 10).should.be.false;
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('some()', () => User.insert([
     {age: 10},
@@ -947,10 +949,11 @@ describe('Model', () => {
     }).should.be.false;
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('populate() - error', () => {
     try {
+      // @ts-ignore
       Post.populate();
     } catch (err) {
       err.message.should.eql('path is required');
@@ -1230,7 +1233,7 @@ describe('Model', () => {
 
     const Test = db.model('Test', schema);
 
-    Test.add({name: 'foo'}).then(data => {
+    (Test as any).add({name: 'foo'}).then(data => {
       data.name.should.eql('foo');
     });
 
diff --git a/test/scripts/query.ts b/test/scripts/query.ts
index 81192205..eca942e7 100644
--- a/test/scripts/query.ts
+++ b/test/scripts/query.ts
@@ -5,6 +5,7 @@ const { sortBy } = lodash;
 import Promise from 'bluebird';
 import Document from '../../dist/document';
 import Database from '../../dist/database';
+import type Query from '../../dist/query';
 
 describe('Query', () => {
 
@@ -29,9 +30,9 @@ describe('Query', () => {
   });
 
   it('count()', () => User.insert(Array(5).fill({})).then(data => {
-    User.find({}).count().should.eql(data.length);
+    (User.find({}) as Query).count().should.eql(data.length);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('forEach()', () => User.insert(Array(5).fill({})).then(data => {
     let count = 0;
@@ -42,67 +43,67 @@ describe('Query', () => {
     });
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('toArray()', () => User.insert(Array(5).fill({})).then(data => {
-    User.find({}).toArray().should.eql(data);
+    (User.find({}) as Query).toArray().should.eql(data);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('eq()', () => User.insert(Array(5).fill({})).then(data => {
     const query = User.find({});
 
     for (let i = 0, len = data.length; i < len; i++) {
-      query.eq(i).should.eql(data[i]);
+      (query as Query).eq(i).should.eql(data[i]);
     }
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('eq() - negative index', () => User.insert(Array(5).fill({})).then(data => {
     const query = User.find({});
 
     for (let i = 1, len = data.length; i <= len; i++) {
-      query.eq(-i).should.eql(data[len - i]);
+      (query as Query).eq(-i).should.eql(data[len - i]);
     }
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('first()', () => User.insert(Array(5).fill({})).then(data => {
-    User.find({}).first().should.eql(data[0]);
+    (User.find({}) as Query).first().should.eql(data[0]);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('last()', () => User.insert(Array(5).fill({})).then(data => {
-    User.find({}).last().should.eql(data[data.length - 1]);
+    (User.find({}) as Query).last().should.eql(data[data.length - 1]);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('slice()', () => User.insert(Array(5).fill({})).then(data => {
-    User.find({}).slice(2, 4).data.should.eql(data.slice(2, 4));
+    (User.find({}) as Query).slice(2, 4).data.should.eql(data.slice(2, 4));
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('limit()', () => User.insert(Array(5).fill({})).then(data => {
-    User.find({}).limit(2).data.should.eql(data.slice(0, 2));
+    (User.find({}) as Query).limit(2).data.should.eql(data.slice(0, 2));
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('skip()', () => User.insert(Array(5).fill({})).then(data => {
-    User.find({}).skip(2).data.should.eql(data.slice(2));
+    (User.find({}) as Query).skip(2).data.should.eql(data.slice(2));
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('reverse()', () => User.insert(Array(5).fill({})).then(data => {
-    User.find({}).reverse().data.should.eql(data.reverse());
+    (User.find({}) as Query).reverse().data.should.eql(data.reverse());
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('shuffle()', () => User.insert(Array(5).fill({})).then(data => {
-    sortBy(User.find({}).shuffle().data, '_id').should.eql(sortBy(data, '_id'));
+    sortBy((User.find({}) as Query).shuffle().data, '_id').should.eql(sortBy(data, '_id'));
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find()', () => User.insert([
     {age: 10},
@@ -111,7 +112,7 @@ describe('Query', () => {
     {age: 30},
     {age: 40}
   ]).then(data => {
-    const query = User.find({}).find({age: 20});
+    const query = (User.find({}) as Query).find({age: 20}) as Query;
     query.data.should.eql(data.slice(1, 3));
 
     const { length } = query;
@@ -120,7 +121,7 @@ describe('Query', () => {
       query.data[i].should.to.be.an.instanceof(Document);
     }
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - blank', () => User.insert([
     {age: 10},
@@ -129,10 +130,10 @@ describe('Query', () => {
     {age: 30},
     {age: 40}
   ]).then(data => {
-    const query = User.find({}).find({});
+    const query = (User.find({}) as Query).find({}) as Query;
     query.data.should.eql(data);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - operator', () => User.insert([
     {age: 10},
@@ -140,10 +141,10 @@ describe('Query', () => {
     {age: 30},
     {age: 40}
   ]).then(data => {
-    const query = User.find({}).find({age: {$gt: 20}});
+    const query = (User.find({}) as Query).find({age: {$gt: 20}}) as Query;
     query.data.should.eql(data.slice(2));
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - limit', () => User.insert([
     {age: 10},
@@ -151,10 +152,10 @@ describe('Query', () => {
     {age: 30},
     {age: 40}
   ]).then(data => {
-    const query = User.find({}).find({age: {$gte: 20}}, {limit: 2});
+    const query = (User.find({}) as Query).find({age: {$gte: 20}}, {limit: 2}) as Query;
     query.data.should.eql(data.slice(1, 3));
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - skip', () => User.insert([
     {age: 10},
@@ -162,15 +163,15 @@ describe('Query', () => {
     {age: 30},
     {age: 40}
   ]).then(data => {
-    let query = User.find({}).find({age: {$gte: 20}}, {skip: 1});
+    let query = (User.find({}) as Query).find({age: {$gte: 20}}, {skip: 1}) as Query;
     query.data.should.eql(data.slice(2));
 
     // with limit
-    query = User.find({}).find({age: {$gte: 20}}, {limit: 1, skip: 1});
+    query = (User.find({}) as Query).find({age: {$gte: 20}}, {limit: 1, skip: 1}) as Query;
     query.data.should.eql(data.slice(2, 3));
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - lean', () => User.insert([
     {age: 10},
@@ -178,127 +179,127 @@ describe('Query', () => {
     {age: 30},
     {age: 40}
   ]).then(data => {
-    const query = User.find({}).find({age: {$gt: 20}}, {lean: true});
+    const query = (User.find({}) as Query).find({age: {$gt: 20}}, {lean: true}) as Query;
     query.should.be.a('array');
     const { length } = query;
     for (let i = 0; i < length; i++) {
       query[i].should.to.not.be.an.instanceof(Document);
     }
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - $and', () => User.insert([
     {name: 'John', age: 20},
     {name: 'John', age: 25},
     {name: 'Jack', age: 30}
   ]).then(data => {
-    const query = User.find({}).find({
+    const query = (User.find({}) as Query).find({
       $and: [
         {name: 'John'},
         {age: {$gt: 20}}
       ]
-    });
+    }) as Query;
 
     query.toArray().should.eql([data[1]]);
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - $or', () => User.insert([
     {name: 'John', age: 20},
     {name: 'John', age: 25},
     {name: 'Jack', age: 30}
   ]).then(data => {
-    const query = User.find({}).find({
+    const query = (User.find({}) as Query).find({
       $or: [
         {name: 'Jack'},
         {age: {$gt: 20}}
       ]
-    });
+    }) as Query;
 
     query.toArray().should.eql(data.slice(1));
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - $nor', () => User.insert([
     {name: 'John', age: 20},
     {name: 'John', age: 25},
     {name: 'Jack', age: 30}
   ]).then(data => {
-    const query = User.find({}).find({
+    const query = (User.find({}) as Query).find({
       $nor: [
         {name: 'Jack'},
         {age: {$gt: 20}}
       ]
-    });
+    }) as Query;
 
     query.toArray().should.eql([data[0]]);
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - $not', () => User.insert([
     {name: 'John', age: 20},
     {name: 'John', age: 25},
     {name: 'Jack', age: 30}
   ]).then(data => {
-    const query = User.find({}).find({
+    const query = (User.find({}) as Query).find({
       $not: {name: 'John'}
-    });
+    }) as Query;
 
     query.toArray().should.eql([data[2]]);
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - $where', () => User.insert([
     {name: 'John', age: 20},
     {name: 'John', age: 25},
     {name: 'Jack', age: 30}
   ]).then(data => {
-    const query = User.find({}).find({
+    const query = (User.find({}) as Query).find({
       $where() {
         return this.name === 'John';
       }
-    });
+    }) as Query;
 
     query.toArray().should.eql(data.slice(0, 2));
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - abnormal - 1', () => User.insert([
     {name: 'John', age: 20},
     {name: 'John', age: 25},
     {name: 'Jack', age: 30}
   ]).then(data => {
-    const query = User.find({}).find({
+    const query = (User.find({}) as Query).find({
       $and: [
         {name: 'Jack'},
         {age: {gt: 20}}
       ]
-    });
+    }) as Query;
     query.toArray().length.should.eql(0);
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('find() - abnormal - 2', () => User.insert([
     {name: 'John', age: 20},
     {name: 'John', age: 25},
     {name: 'Jack', age: 30}
   ]).then(data => {
-    const query = User.find({}).find({
+    const query = (User.find({}) as Query).find({
       $and: [
         {name: 'Jack'},
         {age: {gt: {}}}
       ]
-    });
+    }) as Query;
     query.toArray().should.eql([data[2]]);
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('findOne()', () => User.insert([
     {age: 10},
@@ -306,11 +307,11 @@ describe('Query', () => {
     {age: 30},
     {age: 40}
   ]).then(data => {
-    const result = User.find({}).findOne({age: {$gt: 20}});
+    const result = (User.find({}) as Query).findOne({age: {$gt: 20}});
     result.should.eql(data[2]);
     result.should.to.be.an.instanceof(Document);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('findOne() - lean', () => User.insert([
     {age: 10},
@@ -318,47 +319,47 @@ describe('Query', () => {
     {age: 30},
     {age: 40}
   ]).then(data => {
-    const result = User.find({}).findOne({age: {$gt: 20}}, {lean: true});
+    const result = (User.find({}) as Query).findOne({age: {$gt: 20}}, {lean: true});
     result._id.should.eql(data[2]._id);
     result.should.to.not.be.an.instanceof(Document);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('sort()', () => User.insert([
     {age: 15},
     {age: 35},
     {age: 10}
   ]).then(data => {
-    const query = User.find({}).sort('age');
+    const query = (User.find({}) as Query).sort('age');
     query.data[0].should.eql(data[2]);
     query.data[1].should.eql(data[0]);
     query.data[2].should.eql(data[1]);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('sort() - object', () => Loop.insert([
     {age: {age: 15}},
     {age: {age: 35}},
     {age: {age: 10}}
   ]).then(data => {
-    const query = Loop.find({}).sort('age', { age: 1 });
+    const query = (Loop.find({}) as Query).sort('age', { age: 1 });
     query.data[0].should.eql(data[2]);
     query.data[1].should.eql(data[0]);
     query.data[2].should.eql(data[1]);
     return data;
-  }).map(item => Loop.removeById(item._id)));
+  }).map<unknown, any>(item => Loop.removeById(item._id)));
 
   it('sort() - descending', () => User.insert([
     {age: 15},
     {age: 35},
     {age: 10}
   ]).then(data => {
-    const query = User.find({}).sort('age', -1);
+    const query = (User.find({}) as Query).sort('age', -1);
     query.data[0].should.eql(data[1]);
     query.data[1].should.eql(data[0]);
     query.data[2].should.eql(data[2]);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('sort() - multi', () => User.insert([
     {age: 15, name: 'A'},
@@ -366,13 +367,13 @@ describe('Query', () => {
     {age: 20, name: 'C'},
     {age: 20, name: 'D'}
   ]).then(data => {
-    const query = User.find({}).sort('age name');
+    const query = (User.find({}) as Query).sort('age name');
     query.data[0].should.eql(data[0]);
     query.data[1].should.eql(data[2]);
     query.data[2].should.eql(data[3]);
     query.data[3].should.eql(data[1]);
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('map()', () => User.insert(Array(5).fill({})).then(data => {
     let num = 0;
@@ -387,7 +388,7 @@ describe('Query', () => {
     d1.should.eql(d2);
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('reduce()', () => User.insert([
     {name: 'A'},
@@ -404,7 +405,7 @@ describe('Query', () => {
     sum.name.should.eql('ABC');
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('reduce() - initial', () => User.insert([
     {name: 'A'},
@@ -421,7 +422,7 @@ describe('Query', () => {
     sum.should.eql('_ABC');
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('reduceRight()', () => User.insert([
     {name: 'A'},
@@ -438,7 +439,7 @@ describe('Query', () => {
     sum.name.should.eql('CBA');
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('reduceRight() - initial', () => User.insert([
     {name: 'A'},
@@ -455,7 +456,7 @@ describe('Query', () => {
     sum.should.eql('_CBA');
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('filter()', () => User.insert([
     {age: 10},
@@ -468,12 +469,12 @@ describe('Query', () => {
     const query = User.find({}).filter((data, i) => {
       i.should.eql(num++);
       return data.age > 20;
-    });
+    }) as Query;
 
     query.data.should.eql(data.slice(2));
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('every()', () => User.insert([
     {age: 10},
@@ -491,7 +492,7 @@ describe('Query', () => {
     User.find({}).every((data, i) => data.age > 10).should.be.false;
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('some()', () => User.insert([
     {age: 10},
@@ -509,7 +510,7 @@ describe('Query', () => {
     }).should.be.false;
 
     return data;
-  }).map(item => User.removeById(item._id)));
+  }).map<unknown, any>(item => User.removeById(item._id)));
 
   it('update()', () => User.insert([
     {age: 10},
@@ -517,13 +518,13 @@ describe('Query', () => {
     {age: 30},
     {age: 20},
     {age: 40}
-  ]).then(data => User.find({age: 20}).update({name: 'A'}).then(updated => {
+  ]).then(data => (User.find({age: 20}) as Query).update({name: 'A'}).then(updated => {
     updated[0]._id.should.eql(data[1]._id);
     updated[1]._id.should.eql(data[3]._id);
     updated[0].name.should.eql('A');
     updated[1].name.should.eql('A');
     return data;
-  })).map(item => User.removeById(item._id)));
+  })).map<unknown, any>(item => User.removeById(item._id)));
 
   it('replace()', () => User.insert([
     {age: 10},
@@ -531,13 +532,13 @@ describe('Query', () => {
     {age: 30},
     {age: 20},
     {age: 40}
-  ]).then(data => User.find({age: 20}).replace({name: 'A'}).then(updated => {
+  ]).then(data => (User.find({age: 20}) as Query).replace({name: 'A'}).then(updated => {
     updated[0]._id.should.eql(data[1]._id);
     updated[1]._id.should.eql(data[3]._id);
     updated[0].name.should.eql('A');
     updated[1].name.should.eql('A');
     return data;
-  })).map(item => User.removeById(item._id)));
+  })).map<unknown, any>(item => User.removeById(item._id)));
 
   it('remove()', () => User.insert([
     {age: 10},
@@ -545,11 +546,11 @@ describe('Query', () => {
     {age: 30},
     {age: 20},
     {age: 40}
-  ]).then(data => User.find({age: 20}).remove().then(removed => {
+  ]).then(data => (User.find({age: 20}) as Query).remove().then(removed => {
     should.not.exist(User.findById(data[1]._id));
     should.not.exist(User.findById(data[3]._id));
     return [data[0], data[2], data[4]];
-  })).map(item => User.removeById(item._id)));
+  })).map<unknown, any>(item => User.removeById(item._id)));
 
   it('populate() - object', () => {
     let user, comment;
@@ -562,7 +563,7 @@ describe('Query', () => {
       });
     }).then(comment_ => {
       comment = comment_;
-      return Comment.find({}).populate('author');
+      return (Comment.find({}) as Query).populate('author');
     }).then(result => {
       result.first().author.should.eql(user);
 
@@ -614,7 +615,7 @@ describe('Query', () => {
       });
     }).then(comment_ => {
       comment = comment_;
-      return Comment.find({}).populate(['author']);
+      return (Comment.find({}) as Query).populate(['author']);
     }).then(result => {
       result.first().author.should.eql(user);
 
@@ -636,7 +637,7 @@ describe('Query', () => {
       });
     }).then(comment_ => {
       comment = comment_;
-      return Comment.find({}).populate([{ path: 'author' }]);
+      return (Comment.find({}) as Query).populate([{ path: 'author' }]);
     }).then(result => {
       result.first().author.should.eql(user);
 
@@ -649,7 +650,7 @@ describe('Query', () => {
 
   it('populate() - path is required', () => {
     try {
-      Comment.find({}).populate({});
+      (Comment.find({}) as Query).populate({});
     } catch (err) {
       err.message.should.eql('path is required');
     }
diff --git a/test/scripts/schema.ts b/test/scripts/schema.ts
index 2a4f9a70..7c8fd734 100644
--- a/test/scripts/schema.ts
+++ b/test/scripts/schema.ts
@@ -103,6 +103,7 @@ describe('Schema', () => {
     (() => schema.pre('wtf', () => {})).should.to.throw(TypeError, 'Hook type must be `save` or `remove`!');
 
     // hook is not a function
+    //@ts-ignore
     (() => schema.pre('save', {})).should.to.throw(TypeError, 'Hook must be a function!');
   });
 
@@ -123,6 +124,7 @@ describe('Schema', () => {
     (() => schema.post('wtf', () => {})).should.throw(TypeError, 'Hook type must be `save` or `remove`!');
 
     // hook is not a function
+    //@ts-ignore
     (() => schema.post('save', {})).should.to.throw(TypeError, 'Hook must be a function!');
   });
 
@@ -137,6 +139,7 @@ describe('Schema', () => {
     schema.method.should.to.throw(TypeError, 'Method name is required!');
 
     // without function
+    //@ts-ignore
     (() => schema.method('wtf', {})).should.to.throw(TypeError, 'Instance method must be a function!');
   });
 
@@ -151,6 +154,7 @@ describe('Schema', () => {
     schema.static.should.to.throw(TypeError, 'Method name is required!');
 
     // without function
+    //@ts-ignore
     (() => schema.static('wtf', {})).should.to.throw(TypeError, 'Static method must be a function!');
   });
 });
diff --git a/test/scripts/schematype.ts b/test/scripts/schematype.ts
index a49090e5..39abb55f 100644
--- a/test/scripts/schematype.ts
+++ b/test/scripts/schematype.ts
@@ -4,24 +4,24 @@ import ValidationError from '../../dist/error/validation';
 import SchemaType from '../../dist/schematype';
 
 describe('SchemaType', () => {
-  const type = new SchemaType('test');
+  const type = new SchemaType<number>('test');
 
   it('cast()', () => {
-    type.cast(123).should.eql(123);
+    (type.cast(123) as number).should.eql(123);
   });
 
   it('cast() - default', () => {
     const type = new SchemaType('test', {default: 'foo'});
-    type.cast().should.eql('foo');
+    (type.cast() as string).should.eql('foo');
   });
 
   it('cast() - default - function', () => {
     const type = new SchemaType('test', {default: () => 'foo'});
-    type.cast().should.eql('foo');
+    (type.cast() as string).should.eql('foo');
   });
 
   it('validate()', () => {
-    type.validate(123).should.eql(123);
+    (type.validate(123) as number).should.eql(123);
   });
 
   it('validate() - required', () => {
@@ -127,12 +127,12 @@ describe('SchemaType', () => {
   });
 
   it('u$set', () => {
-    type.u$set(1, 1).should.eql(1);
+    type.u$set<number>(1, 1).should.eql(1);
   });
 
   it('u$unset', () => {
     should.not.exist(type.u$unset(1, true));
-    type.u$unset(1, false).should.eql(1);
+    (type.u$unset<number>(1, false) as number).should.eql(1);
   });
 
   it('u$rename', () => {
diff --git a/test/scripts/types/array.ts b/test/scripts/types/array.ts
index 19ba5313..61cd52ba 100644
--- a/test/scripts/types/array.ts
+++ b/test/scripts/types/array.ts
@@ -13,12 +13,12 @@ describe('SchemaTypeArray', () => {
     type.cast('foo').should.eql(['foo']);
     type.cast([]).should.eql([]);
     type.cast([1, 2, 3]).should.eql([1, 2, 3]);
-    type.cast().should.eql([]);
+    (type.cast() as any[]).should.eql([]);
   });
 
   it('cast() - default', () => {
     const type = new SchemaTypeArray('test', {default: [1, 2, 3]});
-    type.cast().should.eql([1, 2, 3]);
+    (type.cast() as any[]).should.eql([1, 2, 3]);
   });
 
   it('cast() - child', () => {
diff --git a/test/scripts/types/buffer.ts b/test/scripts/types/buffer.ts
index 9bae4b19..a9fa0d68 100644
--- a/test/scripts/types/buffer.ts
+++ b/test/scripts/types/buffer.ts
@@ -25,7 +25,7 @@ describe('SchemaTypeBuffer', () => {
     const buf = Buffer.from([97, 98, 99]);
     const type = new SchemaTypeBuffer('test', {default: buf});
 
-    type.cast().should.eql(buf);
+    (type.cast() as Buffer).should.eql(buf);
   });
 
   function shouldThrowError(value) {
@@ -50,7 +50,9 @@ describe('SchemaTypeBuffer', () => {
   it('match()', () => {
     type.match(Buffer.from([97, 98, 99]), Buffer.from([97, 98, 99])).should.be.true;
     type.match(Buffer.from([97, 98, 99]), Buffer.from([97, 98, 100])).should.be.false;
+    //@ts-ignore
     type.match(undefined, Buffer.from([97, 98, 99])).should.be.false;
+    //@ts-ignore
     type.match(undefined, undefined).should.be.true;
   });
 
diff --git a/test/scripts/types/date.ts b/test/scripts/types/date.ts
index da80826b..b0d73bf6 100644
--- a/test/scripts/types/date.ts
+++ b/test/scripts/types/date.ts
@@ -16,7 +16,7 @@ describe('SchemaTypeDate', () => {
     const date = new Date();
     const type = new SchemaTypeDate('test', {default: date});
 
-    type.cast().should.eql(date);
+    (type.cast() as Date).should.eql(date);
   });
 
   function shouldThrowError(value) {
@@ -42,7 +42,9 @@ describe('SchemaTypeDate', () => {
   it('match()', () => {
     type.match(new Date(2014, 1, 1), new Date(2014, 1, 1)).should.be.true;
     type.match(new Date(2014, 1, 1), new Date(2014, 1, 2)).should.be.false;
+    //@ts-ignore
     type.match(undefined, new Date()).should.be.false;
+    //@ts-ignore
     type.match(undefined, undefined).should.be.true;
   });
 
diff --git a/test/scripts/types/enum.ts b/test/scripts/types/enum.ts
index ded35ace..7804322b 100644
--- a/test/scripts/types/enum.ts
+++ b/test/scripts/types/enum.ts
@@ -7,7 +7,7 @@ describe('SchemaTypeEnum', () => {
   it('validate()', () => {
     const type = new SchemaTypeEnum('test', {elements: ['foo', 'bar', 'baz']});
 
-    type.validate('foo').should.eql('foo');
+    (type.validate('foo') as string).should.eql('foo');
 
     (() => type.validate('wat')).should.to.throw(ValidationError, 'The value must be one of foo, bar, baz');
   });
diff --git a/test/scripts/types/number.ts b/test/scripts/types/number.ts
index ae56afbf..3dd6003b 100644
--- a/test/scripts/types/number.ts
+++ b/test/scripts/types/number.ts
@@ -17,7 +17,7 @@ describe('SchemaTypeNumber', () => {
 
   it('cast() - default', () => {
     const type = new SchemaTypeNumber('type', {default: 42});
-    type.cast().should.eql(42);
+    (type.cast() as number).should.eql(42);
   });
 
   function shouldThrowError(value) {
diff --git a/test/scripts/types/object.ts b/test/scripts/types/object.ts
index e29b6473..960b651c 100644
--- a/test/scripts/types/object.ts
+++ b/test/scripts/types/object.ts
@@ -6,6 +6,6 @@ describe('SchemaTypeObject', () => {
   const type = new SchemaTypeObject('test');
 
   it('cast() - default', () => {
-    type.cast().should.eql({});
+    (type.cast() as object).should.eql({});
   });
 });
diff --git a/test/scripts/types/string.ts b/test/scripts/types/string.ts
index b2572c8c..ebbda208 100644
--- a/test/scripts/types/string.ts
+++ b/test/scripts/types/string.ts
@@ -21,7 +21,7 @@ describe('SchemaTypeString', () => {
 
   it('cast() - default', () => {
     const type = new SchemaTypeString('test', {default: 'foo'});
-    type.cast().should.eql('foo');
+    (type.cast() as string).should.eql('foo');
   });
 
   function shouldThrowError(value) {
diff --git a/test/scripts/types/virtual.ts b/test/scripts/types/virtual.ts
index ddbc83c5..a7e25d47 100644
--- a/test/scripts/types/virtual.ts
+++ b/test/scripts/types/virtual.ts
@@ -9,10 +9,11 @@ describe('SchemaTypeVirtual', () => {
     const getter = () => 'foo';
 
     type.get(getter);
-    type.getter.should.eql(getter);
+    (type.getter as () => any).should.eql(getter);
   });
 
   it('get() - type check', () => {
+    //@ts-ignore
     (() => type.get(123)).should.to.throw(TypeError, 'Getter must be a function!');
   });
 
@@ -22,10 +23,11 @@ describe('SchemaTypeVirtual', () => {
     };
 
     type.set(setter);
-    type.setter.should.eql(setter);
+    (type.setter as () => any).should.eql(setter);
   });
 
   it('set() - type check', () => {
+    //@ts-ignore
     (() => type.set(123)).should.to.throw(TypeError, 'Setter must be a function!');
   });