diff --git a/README.md b/README.md
index 20fc58ec..bc92ad7f 100644
--- a/README.md
+++ b/README.md
@@ -371,7 +371,7 @@ Returns the second element or undefined when there are less than two elements in
 
 <!-- prettier-ignore-start -->
 ```typescript
-([, x]: [any, any]) => any
+([, x]: any[]) => any
 ```
 <!-- prettier-ignore-end -->
 
@@ -573,21 +573,21 @@ Runs the given tasks in a sequence.
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  now: any
+  now: string | number | Date
 ) => (
   {
     endedAt: aEnd,
     startedAt: aStart
   }: {
-    endedAt: any;
-    startedAt: any;
+    endedAt: string | number | Date;
+    startedAt: string | number | Date;
   },
   {
     endedAt: bEnd,
     startedAt: bStart
   }: {
-    endedAt: any;
-    startedAt: any;
+    endedAt: string | number | Date;
+    startedAt: string | number | Date;
   }
 ) => number
 ```
@@ -599,7 +599,10 @@ Runs the given tasks in a sequence.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(min: any, max: any) => (dateStringOrDate: any) => Date
+(
+  min: number | Date,
+  max: number | Date
+) => (dateStringOrDate: string | number | Date) => Date
 ```
 <!-- prettier-ignore-end -->
 
@@ -609,7 +612,10 @@ Runs the given tasks in a sequence.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(a: any, b: any) => number
+(
+  a: string | number | Date,
+  b: string | number | Date
+) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -619,7 +625,10 @@ Runs the given tasks in a sequence.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(from: any, to: any) => (date?: Date) => boolean
+(
+  from: string | number | Date,
+  to: string | number | Date
+) => (date?: Date) => boolean
 ```
 <!-- prettier-ignore-end -->
 
@@ -639,7 +648,7 @@ Runs the given tasks in a sequence.
   local?: boolean;
   now?: Date;
   timezoneOffset?: number;
-}) => (date: any) => any[]
+}) => (date?: string | number | Date) => string[]
 ```
 <!-- prettier-ignore-end -->
 
@@ -649,7 +658,22 @@ Runs the given tasks in a sequence.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(leapYear: any) => number[]
+(
+  leapYear: boolean
+) => [
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number
+]
 ```
 <!-- prettier-ignore-end -->
 
@@ -659,7 +683,7 @@ Runs the given tasks in a sequence.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(year: any) => number
+(year: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -669,7 +693,7 @@ Runs the given tasks in a sequence.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(monthIndex: any) => string
+(monthIndex: number) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -679,7 +703,10 @@ Runs the given tasks in a sequence.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(source: any, showSeconds: any) => string
+(
+  source: [number, number, number],
+  showSeconds: boolean
+) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -690,7 +717,7 @@ Runs the given tasks in a sequence.
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  date: any,
+  date: string | number | Date,
   timezoneOffset?: number,
   local?: boolean
 ) => Date
@@ -703,7 +730,7 @@ Runs the given tasks in a sequence.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(sourceDate: any, timezoneOffset?: number) => string
+(sourceDate: Date, timezoneOffset?: number) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -714,7 +741,7 @@ Runs the given tasks in a sequence.
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  sourceDate: any,
+  sourceDate: Date,
   showSeconds?: boolean,
   timezoneOffset?: number
 ) => string
@@ -728,7 +755,7 @@ Runs the given tasks in a sequence.
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  sourceDate: any,
+  sourceDate: Date,
   showDay?: boolean,
   timezoneOffset?: number
 ) => string
@@ -741,7 +768,7 @@ Runs the given tasks in a sequence.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(duration: any, showSeconds?: boolean) => string
+(duration: number, showSeconds?: boolean) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -752,7 +779,7 @@ Runs the given tasks in a sequence.
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  sourceDate: any,
+  sourceDate: Date,
   showSeconds?: boolean,
   timezoneOffset?: number
 ) => string
@@ -765,7 +792,7 @@ Runs the given tasks in a sequence.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(days: any) => number
+(days: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -775,7 +802,7 @@ Runs the given tasks in a sequence.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(hours: any) => number
+(hours: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -785,7 +812,7 @@ Runs the given tasks in a sequence.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(minutes: any) => number
+(minutes: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -795,7 +822,7 @@ Runs the given tasks in a sequence.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(seconds: any) => number
+(seconds: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -805,7 +832,7 @@ Runs the given tasks in a sequence.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(...xs: any[]) => string
+(...xs: string[]) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -815,7 +842,7 @@ Runs the given tasks in a sequence.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(year: any) => boolean
+(year: number) => boolean
 ```
 <!-- prettier-ignore-end -->
 
@@ -835,7 +862,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(date: any) => Date
+(date: number | Date) => Date
 ```
 <!-- prettier-ignore-end -->
 
@@ -855,7 +882,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(dateTimeString: any) => any
+(dateTimeString: string) => string[]
 ```
 <!-- prettier-ignore-end -->
 
@@ -866,7 +893,7 @@ string[]
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  date: any,
+  date: string | number | Date,
   timezoneOffset?: number,
   local?: boolean
 ) => Date
@@ -879,7 +906,10 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(sourceDate: any, numberOfDays: any) => Date
+(
+  sourceDate: string | number | Date,
+  numberOfDays: number
+) => Date
 ```
 <!-- prettier-ignore-end -->
 
@@ -889,7 +919,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(date: any) => string
+(date: Date) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -899,7 +929,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(xs: any) => any
+(xs: (string | number | Date)[]) => Date[]
 ```
 <!-- prettier-ignore-end -->
 
@@ -909,7 +939,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(milliseconds: any) => number
+(milliseconds: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -919,7 +949,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(milliseconds: any) => number
+(milliseconds: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -929,7 +959,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(x: any) => any
+(x: Date) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -939,7 +969,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(date: any) => string
+(date: Date) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -949,7 +979,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(date: any, timezoneOffset?: number) => Date
+(date: Date, timezoneOffset?: number) => Date
 ```
 <!-- prettier-ignore-end -->
 
@@ -959,7 +989,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(milliseconds: any) => number
+(milliseconds: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -969,7 +999,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(milliseconds: any) => number
+(milliseconds: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -979,7 +1009,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(date: any) => boolean
+(date?: any) => boolean
 ```
 <!-- prettier-ignore-end -->
 
@@ -1008,7 +1038,14 @@ Computes a difference between two objects.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(obj1: object, obj2: object) => object
+(
+  obj1?: {
+    [index: string]: any;
+  },
+  obj2?: {
+    [index: string]: any;
+  }
+) => object
 ```
 <!-- prettier-ignore-end -->
 
@@ -1023,15 +1060,7 @@ Provides a way to encode strings and bytes from and into Base64URL.
 <!-- prettier-ignore-start -->
 ```typescript
 {
-  decode: (
-    text: string,
-    context?: {
-      atob: (byteString: string) => string;
-      TextDecoder: new (encoding: string) => {
-        decode: (input?: Uint8Array) => string;
-      };
-    }
-  ) => string;
+  decode: (text: string, context?: DecodeContext) => string;
   decodeBytes: (
     text: string,
     context?: {
@@ -1050,15 +1079,7 @@ Provides a way to encode strings and bytes from and into Base64URL.
       };
     }
   ) => string;
-  encodeBytes: (
-    bytes: number[],
-    context?: {
-      btoa: (byteString: string) => string;
-      TextEncoder: new () => {
-        encode: (input?: string) => Uint8Array;
-      };
-    }
-  ) => string;
+  encodeBytes: (bytes: number[], context?: EncodeContext) => string;
   fromByteString: (byteString: string) => number[];
   toByteString: (bytes: number[]) => string;
 }
@@ -1319,6 +1340,18 @@ Checks if given value is an integer.
 ```
 <!-- prettier-ignore-end -->
 
+#### nonNullable
+
+Checks and asserts the given value is not a null or undefined.
+
+##### Type signature
+
+<!-- prettier-ignore-start -->
+```typescript
+<T>(val: T) => val is NonNullable<T>
+```
+<!-- prettier-ignore-end -->
+
 #### normal
 
 Checks if the given value is a number in a normal range [0, 1].
@@ -1865,7 +1898,12 @@ Merges two objects deeply.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(a: object, b: object) => object
+(
+  a: {
+    [index: string]: any;
+  },
+  b: object
+) => object
 ```
 <!-- prettier-ignore-end -->
 
@@ -1909,7 +1947,9 @@ Sorts the given object by a comparator.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(f: any) => (xs: any) => object
+(
+  f: (a: any, b: any) => number
+) => (xs: object) => object
 ```
 <!-- prettier-ignore-end -->
 
@@ -1947,7 +1987,7 @@ Serializes the given object into a query string.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(xs?: {}) => string
+(xs?: { [index: string]: any }) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -1961,7 +2001,7 @@ Checks if the given range is empty.
 
 <!-- prettier-ignore-start -->
 ```typescript
-([min, max]: [any, any]) => boolean
+([min, max]: [number, number]) => boolean
 ```
 <!-- prettier-ignore-end -->
 
@@ -1982,7 +2022,10 @@ Checks if the given ranges are equal.
 
 <!-- prettier-ignore-start -->
 ```typescript
-([a, b]: [any, any], [c, d]: [any, any]) => boolean
+(
+  [a, b]: [number, number],
+  [c, d]: [number, number]
+) => boolean
 ```
 <!-- prettier-ignore-end -->
 
@@ -1994,7 +2037,7 @@ Computes the signed length of the given range.
 
 <!-- prettier-ignore-start -->
 ```typescript
-([min, max]: [any, any]) => number
+([min, max]: [number, number]) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -2177,7 +2220,10 @@ Calculates a cross product of the given vectors. Returns a scalar.
 
 <!-- prettier-ignore-start -->
 ```typescript
-([a, b]: [any, any], [c, d]: [any, any]) => number
+(
+  [a, b]: [number, number],
+  [c, d]: [number, number]
+) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -2189,7 +2235,10 @@ Calculates a dot product of the given vectors. Returns a scalar.
 
 <!-- prettier-ignore-start -->
 ```typescript
-([a, b]: [any, any], [c, d]: [any, any]) => number
+(
+  [a, b]: [number, number],
+  [c, d]: [number, number]
+) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -2278,7 +2327,7 @@ Normalizes the given vector. Returns [0, 0] vector for points.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(vector: [number, number]) => number[]
+(vector: [number, number]) => [number, number]
 ```
 <!-- prettier-ignore-end -->
 
@@ -2452,10 +2501,10 @@ Tests if the current event seems like an intent to open a new tab. Useful for cl
   metaKey,
   shiftKey
 }: {
-  button: any;
-  ctrlKey: any;
-  metaKey: any;
-  shiftKey: any;
+  button?: number;
+  ctrlKey?: boolean;
+  metaKey?: boolean;
+  shiftKey?: boolean;
 }) => boolean
 ```
 <!-- prettier-ignore-end -->
diff --git a/array/README.md b/array/README.md
index b1bc4adb..28e53f64 100644
--- a/array/README.md
+++ b/array/README.md
@@ -360,7 +360,7 @@ Returns the second element or undefined when there are less than two elements in
 
 <!-- prettier-ignore-start -->
 ```typescript
-([, x]: [any, any]) => any
+([, x]: any[]) => any
 ```
 <!-- prettier-ignore-end -->
 
diff --git a/array/differs.js b/array/differs.js
index af794c77..7ea5ae73 100644
--- a/array/differs.js
+++ b/array/differs.js
@@ -1,5 +1,9 @@
+import isNonNullable from "../is/nonNullable.js";
+
 export default (xs, ys) =>
   Boolean(!xs && ys) ||
   Boolean(!ys && xs) ||
+  !isNonNullable(ys) ||
+  !isNonNullable(xs) ||
   xs.length !== ys.length ||
   xs.some((x, index) => x !== ys[index]);
diff --git a/array/differs.test.ts b/array/differs.test.ts
index dde1b8a9..82e1bfbf 100644
--- a/array/differs.test.ts
+++ b/array/differs.test.ts
@@ -11,6 +11,8 @@ describe("differs", () => {
   it("short-circuits over parameter presence", () => {
     expect(differs(null, [1, 2])).toBe(true);
     expect(differs([2, 3], undefined)).toBe(true);
+    expect(differs(null, null)).toBe(true);
+    expect(differs(undefined, undefined)).toBe(true);
   });
 
   it("compares elements index-wise", () => {
diff --git a/array/differs.ts b/array/differs.ts
index 51d620fd..6228d015 100644
--- a/array/differs.ts
+++ b/array/differs.ts
@@ -1,5 +1,9 @@
+import isNonNullable from "../is/nonNullable";
+
 export default (xs?: any[], ys?: any[]) =>
   Boolean(!xs && ys) ||
   Boolean(!ys && xs) ||
+  !isNonNullable(ys) ||
+  !isNonNullable(xs) ||
   xs.length !== ys.length ||
   xs.some((x, index) => x !== ys[index]);
diff --git a/array/first.ts b/array/first.ts
index 42b96520..82aedf95 100644
--- a/array/first.ts
+++ b/array/first.ts
@@ -1 +1 @@
-export default ([x]) => x;
+export default ([x]: [any]) => x;
diff --git a/array/second.json b/array/second.json
index 0b9838fe..e5fb2002 100644
--- a/array/second.json
+++ b/array/second.json
@@ -1,7 +1,7 @@
 {
   "name": "second",
   "description": "Returns the second element or undefined when there are less than two elements in the given array.",
-  "signature": "([, x]: [any, any]) => any",
+  "signature": "([, x]: any[]) => any",
   "examples": [
     {
       "language": "javascript",
diff --git a/array/second.md b/array/second.md
index 7917e7c8..d05ce695 100644
--- a/array/second.md
+++ b/array/second.md
@@ -6,6 +6,6 @@ Returns the second element or undefined when there are less than two elements in
 
 <!-- prettier-ignore-start -->
 ```typescript
-([, x]: [any, any]) => any
+([, x]: any[]) => any
 ```
 <!-- prettier-ignore-end -->
diff --git a/array/second.ts b/array/second.ts
index 41953d02..623dd03d 100644
--- a/array/second.ts
+++ b/array/second.ts
@@ -1 +1 @@
-export default ([, x]) => x;
+export default ([, x]: any[]): any => x;
diff --git a/async/debounce.ts b/async/debounce.ts
index cb278823..e264751f 100644
--- a/async/debounce.ts
+++ b/async/debounce.ts
@@ -1,7 +1,7 @@
 /* eslint-env browser */
 
 export default (f: { (...args: any[]): any }, wait: number) => {
-  let timeout;
+  let timeout: any;
 
   return (...args: any[]) => {
     const resolve = () => {
diff --git a/compile.js b/compile.js
index b2eeff10..88cb1f3f 100644
--- a/compile.js
+++ b/compile.js
@@ -68,27 +68,51 @@ const main = async cwd => {
         "--skipLibCheck",
         "--module ES6",
         "--target ES2020",
+        "--noImplicitAny",
+        "--strict",
         "-d",
         quotePath(path.posix.normalize(filePath))
       ];
 
       const command = [executable, ...args].join(" ");
 
-      console.time(command);
-
       const windows = process.platform === "win32";
 
-      const { stdout, stderr } = await execAsync(command, {
+      const execOptions = {
         windowsVerbatimArguments: windows
-      });
+      };
+
+      console.time(command);
+
+      const { stdout, stderr } = await execAsync(command, execOptions);
 
       console.timeEnd(command);
 
-      console.log(`Compiled ${relativeFilePath}`);
+      console.log(`Compiled with strict mode ${relativeFilePath}`);
 
       if (stdout || stderr) {
         console.log({ stdout, stderr });
       }
+
+      const nonStrictCommand = [
+        executable,
+        ...args.filter(x => x !== "--strict")
+      ].join(" ");
+
+      console.time(nonStrictCommand);
+
+      const { stdout: secondStdout, stderr: secondStderr } = await execAsync(
+        nonStrictCommand,
+        execOptions
+      );
+
+      console.timeEnd(nonStrictCommand);
+
+      console.log(`Compiled without strict mode ${relativeFilePath}`);
+
+      if (secondStdout || secondStderr) {
+        console.log({ secondStdout, secondStderr });
+      }
     } catch (error) {
       console.error(error);
 
diff --git a/date/README.md b/date/README.md
index d5cb0a97..46c3f123 100644
--- a/date/README.md
+++ b/date/README.md
@@ -5,21 +5,21 @@
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  now: any
+  now: string | number | Date
 ) => (
   {
     endedAt: aEnd,
     startedAt: aStart
   }: {
-    endedAt: any;
-    startedAt: any;
+    endedAt: string | number | Date;
+    startedAt: string | number | Date;
   },
   {
     endedAt: bEnd,
     startedAt: bStart
   }: {
-    endedAt: any;
-    startedAt: any;
+    endedAt: string | number | Date;
+    startedAt: string | number | Date;
   }
 ) => number
 ```
@@ -31,7 +31,10 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(min: any, max: any) => (dateStringOrDate: any) => Date
+(
+  min: number | Date,
+  max: number | Date
+) => (dateStringOrDate: string | number | Date) => Date
 ```
 <!-- prettier-ignore-end -->
 
@@ -41,7 +44,10 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(a: any, b: any) => number
+(
+  a: string | number | Date,
+  b: string | number | Date
+) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -51,7 +57,10 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(from: any, to: any) => (date?: Date) => boolean
+(
+  from: string | number | Date,
+  to: string | number | Date
+) => (date?: Date) => boolean
 ```
 <!-- prettier-ignore-end -->
 
@@ -71,7 +80,7 @@
   local?: boolean;
   now?: Date;
   timezoneOffset?: number;
-}) => (date: any) => any[]
+}) => (date?: string | number | Date) => string[]
 ```
 <!-- prettier-ignore-end -->
 
@@ -81,7 +90,22 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(leapYear: any) => number[]
+(
+  leapYear: boolean
+) => [
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number
+]
 ```
 <!-- prettier-ignore-end -->
 
@@ -91,7 +115,7 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(year: any) => number
+(year: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -101,7 +125,7 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(monthIndex: any) => string
+(monthIndex: number) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -111,7 +135,10 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(source: any, showSeconds: any) => string
+(
+  source: [number, number, number],
+  showSeconds: boolean
+) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -122,7 +149,7 @@
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  date: any,
+  date: string | number | Date,
   timezoneOffset?: number,
   local?: boolean
 ) => Date
@@ -135,7 +162,7 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(sourceDate: any, timezoneOffset?: number) => string
+(sourceDate: Date, timezoneOffset?: number) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -146,7 +173,7 @@
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  sourceDate: any,
+  sourceDate: Date,
   showSeconds?: boolean,
   timezoneOffset?: number
 ) => string
@@ -160,7 +187,7 @@
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  sourceDate: any,
+  sourceDate: Date,
   showDay?: boolean,
   timezoneOffset?: number
 ) => string
@@ -173,7 +200,7 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(duration: any, showSeconds?: boolean) => string
+(duration: number, showSeconds?: boolean) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -184,7 +211,7 @@
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  sourceDate: any,
+  sourceDate: Date,
   showSeconds?: boolean,
   timezoneOffset?: number
 ) => string
@@ -197,7 +224,7 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(days: any) => number
+(days: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -207,7 +234,7 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(hours: any) => number
+(hours: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -217,7 +244,7 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(minutes: any) => number
+(minutes: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -227,7 +254,7 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(seconds: any) => number
+(seconds: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -237,7 +264,7 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(...xs: any[]) => string
+(...xs: string[]) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -247,7 +274,7 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(year: any) => boolean
+(year: number) => boolean
 ```
 <!-- prettier-ignore-end -->
 
@@ -267,7 +294,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(date: any) => Date
+(date: number | Date) => Date
 ```
 <!-- prettier-ignore-end -->
 
@@ -287,7 +314,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(dateTimeString: any) => any
+(dateTimeString: string) => string[]
 ```
 <!-- prettier-ignore-end -->
 
@@ -298,7 +325,7 @@ string[]
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  date: any,
+  date: string | number | Date,
   timezoneOffset?: number,
   local?: boolean
 ) => Date
@@ -311,7 +338,10 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(sourceDate: any, numberOfDays: any) => Date
+(
+  sourceDate: string | number | Date,
+  numberOfDays: number
+) => Date
 ```
 <!-- prettier-ignore-end -->
 
@@ -321,7 +351,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(date: any) => string
+(date: Date) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -331,7 +361,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(xs: any) => any
+(xs: (string | number | Date)[]) => Date[]
 ```
 <!-- prettier-ignore-end -->
 
@@ -341,7 +371,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(milliseconds: any) => number
+(milliseconds: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -351,7 +381,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(milliseconds: any) => number
+(milliseconds: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -361,7 +391,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(x: any) => any
+(x: Date) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -371,7 +401,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(date: any) => string
+(date: Date) => string
 ```
 <!-- prettier-ignore-end -->
 
@@ -381,7 +411,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(date: any, timezoneOffset?: number) => Date
+(date: Date, timezoneOffset?: number) => Date
 ```
 <!-- prettier-ignore-end -->
 
@@ -391,7 +421,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(milliseconds: any) => number
+(milliseconds: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -401,7 +431,7 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(milliseconds: any) => number
+(milliseconds: number) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -411,6 +441,6 @@ string[]
 
 <!-- prettier-ignore-start -->
 ```typescript
-(date: any) => boolean
+(date?: any) => boolean
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/byDateWithFallback.json b/date/byDateWithFallback.json
index f611cceb..f045e83e 100644
--- a/date/byDateWithFallback.json
+++ b/date/byDateWithFallback.json
@@ -1,7 +1,7 @@
 {
   "name": "byDateWithFallback",
   "description": "TODO: Fill short description here.",
-  "signature": "(\n  now: any\n) => (\n  {\n    endedAt: aEnd,\n    startedAt: aStart\n  }: {\n    endedAt: any;\n    startedAt: any;\n  },\n  {\n    endedAt: bEnd,\n    startedAt: bStart\n  }: {\n    endedAt: any;\n    startedAt: any;\n  }\n) => number",
+  "signature": "(\n  now: string | number | Date\n) => (\n  {\n    endedAt: aEnd,\n    startedAt: aStart\n  }: {\n    endedAt: string | number | Date;\n    startedAt: string | number | Date;\n  },\n  {\n    endedAt: bEnd,\n    startedAt: bStart\n  }: {\n    endedAt: string | number | Date;\n    startedAt: string | number | Date;\n  }\n) => number",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/byDateWithFallback.md b/date/byDateWithFallback.md
index 6d938882..df10b168 100644
--- a/date/byDateWithFallback.md
+++ b/date/byDateWithFallback.md
@@ -5,21 +5,21 @@
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  now: any
+  now: string | number | Date
 ) => (
   {
     endedAt: aEnd,
     startedAt: aStart
   }: {
-    endedAt: any;
-    startedAt: any;
+    endedAt: string | number | Date;
+    startedAt: string | number | Date;
   },
   {
     endedAt: bEnd,
     startedAt: bStart
   }: {
-    endedAt: any;
-    startedAt: any;
+    endedAt: string | number | Date;
+    startedAt: string | number | Date;
   }
 ) => number
 ```
diff --git a/date/byDateWithFallback.ts b/date/byDateWithFallback.ts
index 3c6c5296..85c42ed5 100644
--- a/date/byDateWithFallback.ts
+++ b/date/byDateWithFallback.ts
@@ -1,6 +1,12 @@
-export default now => (
-  { endedAt: aEnd, startedAt: aStart },
-  { endedAt: bEnd, startedAt: bStart }
+export default (now: Date | string | number) => (
+  {
+    endedAt: aEnd,
+    startedAt: aStart
+  }: { endedAt: Date | string | number; startedAt: Date | string | number },
+  {
+    endedAt: bEnd,
+    startedAt: bStart
+  }: { endedAt: Date | string | number; startedAt: Date | string | number }
 ) => {
   const aEndDate = new Date(aEnd || now);
   const aStartDate = new Date(aStart || now);
diff --git a/date/clamp.json b/date/clamp.json
index 53da8bbf..93413be6 100644
--- a/date/clamp.json
+++ b/date/clamp.json
@@ -1,7 +1,7 @@
 {
   "name": "clamp",
   "description": "TODO: Fill short description here.",
-  "signature": "(min: any, max: any) => (dateStringOrDate: any) => Date",
+  "signature": "(\n  min: number | Date,\n  max: number | Date\n) => (dateStringOrDate: string | number | Date) => Date",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/clamp.md b/date/clamp.md
index 4e872f0d..012878c8 100644
--- a/date/clamp.md
+++ b/date/clamp.md
@@ -4,6 +4,9 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(min: any, max: any) => (dateStringOrDate: any) => Date
+(
+  min: number | Date,
+  max: number | Date
+) => (dateStringOrDate: string | number | Date) => Date
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/clamp.ts b/date/clamp.ts
index 51fd80cd..e8115276 100644
--- a/date/clamp.ts
+++ b/date/clamp.ts
@@ -1,4 +1,6 @@
-export default (min, max) => dateStringOrDate => {
+export default (min: Date | number, max: Date | number) => (
+  dateStringOrDate: string | number | Date
+) => {
   const date = new Date(dateStringOrDate);
 
   const clamped = new Date(
diff --git a/date/dateDiff.json b/date/dateDiff.json
index 913e706c..a6d66fda 100644
--- a/date/dateDiff.json
+++ b/date/dateDiff.json
@@ -1,7 +1,7 @@
 {
   "name": "dateDiff",
   "description": "TODO: Fill short description here.",
-  "signature": "(a: any, b: any) => number",
+  "signature": "(\n  a: string | number | Date,\n  b: string | number | Date\n) => number",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/dateDiff.md b/date/dateDiff.md
index cba3b9dd..ebc6761f 100644
--- a/date/dateDiff.md
+++ b/date/dateDiff.md
@@ -4,6 +4,9 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(a: any, b: any) => number
+(
+  a: string | number | Date,
+  b: string | number | Date
+) => number
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/dateDiff.ts b/date/dateDiff.ts
index 2e4d2ce6..d8e585a3 100644
--- a/date/dateDiff.ts
+++ b/date/dateDiff.ts
@@ -1,4 +1,4 @@
-export default (a, b) => {
+export default (a: string | number | Date, b: string | number | Date) => {
   const d1 = new Date(a);
   const d2 = new Date(b);
 
diff --git a/date/dateInRange.json b/date/dateInRange.json
index ef4edab0..db7e8e6e 100644
--- a/date/dateInRange.json
+++ b/date/dateInRange.json
@@ -1,7 +1,7 @@
 {
   "name": "dateInRange",
   "description": "TODO: Fill short description here.",
-  "signature": "(from: any, to: any) => (date?: Date) => boolean",
+  "signature": "(\n  from: string | number | Date,\n  to: string | number | Date\n) => (date?: Date) => boolean",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/dateInRange.md b/date/dateInRange.md
index 115a6199..067db71b 100644
--- a/date/dateInRange.md
+++ b/date/dateInRange.md
@@ -4,6 +4,9 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(from: any, to: any) => (date?: Date) => boolean
+(
+  from: string | number | Date,
+  to: string | number | Date
+) => (date?: Date) => boolean
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/dateInRange.ts b/date/dateInRange.ts
index 29997ef7..25859e6c 100644
--- a/date/dateInRange.ts
+++ b/date/dateInRange.ts
@@ -1,4 +1,6 @@
-export default (from, to) => (date = new Date()) => {
+export default (from: string | number | Date, to: string | number | Date) => (
+  date = new Date()
+) => {
   const dateTime = new Date(date).getTime();
   const fromTime = new Date(from).getTime();
   const toTime = new Date(to).getTime();
diff --git a/date/dayRange.json b/date/dayRange.json
index 9d5d6503..76b43def 100644
--- a/date/dayRange.json
+++ b/date/dayRange.json
@@ -1,7 +1,7 @@
 {
   "name": "dayRange",
   "description": "TODO: Fill short description here.",
-  "signature": "({\n  iso,\n  local,\n  now,\n  timezoneOffset\n}: {\n  iso?: boolean;\n  local?: boolean;\n  now?: Date;\n  timezoneOffset?: number;\n}) => (date: any) => any[]",
+  "signature": "({\n  iso,\n  local,\n  now,\n  timezoneOffset\n}: {\n  iso?: boolean;\n  local?: boolean;\n  now?: Date;\n  timezoneOffset?: number;\n}) => (date?: string | number | Date) => string[]",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/dayRange.md b/date/dayRange.md
index d6729e2c..a0aa3418 100644
--- a/date/dayRange.md
+++ b/date/dayRange.md
@@ -14,6 +14,6 @@
   local?: boolean;
   now?: Date;
   timezoneOffset?: number;
-}) => (date: any) => any[]
+}) => (date?: string | number | Date) => string[]
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/dayRange.ts b/date/dayRange.ts
index 62c9f654..cab26edc 100644
--- a/date/dayRange.ts
+++ b/date/dayRange.ts
@@ -10,7 +10,7 @@ export default ({
   local = true,
   now = new Date(),
   timezoneOffset = 0
-}) => date => {
+}) => (date?: string | number | Date) => {
   const convert = iso ? toISO : toISOFromLocalDateTime;
 
   const [start] = splitDateTime(
diff --git a/date/daysInMonths.json b/date/daysInMonths.json
index 9f0cfdad..83aeb8f5 100644
--- a/date/daysInMonths.json
+++ b/date/daysInMonths.json
@@ -1,7 +1,7 @@
 {
   "name": "daysInMonths",
   "description": "TODO: Fill short description here.",
-  "signature": "(leapYear: any) => number[]",
+  "signature": "(\n  leapYear: boolean\n) => [\n  number,\n  number,\n  number,\n  number,\n  number,\n  number,\n  number,\n  number,\n  number,\n  number,\n  number,\n  number\n]",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/daysInMonths.md b/date/daysInMonths.md
index b5b51fee..620aa894 100644
--- a/date/daysInMonths.md
+++ b/date/daysInMonths.md
@@ -4,6 +4,21 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(leapYear: any) => number[]
+(
+  leapYear: boolean
+) => [
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number
+]
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/daysInMonths.ts b/date/daysInMonths.ts
index 2ad5657f..571a118f 100644
--- a/date/daysInMonths.ts
+++ b/date/daysInMonths.ts
@@ -1,14 +1,16 @@
-export default leapYear => [
-  31,
-  leapYear ? 29 : 28,
-  31,
-  30,
-  31,
-  30,
-  31,
-  31,
-  30,
-  31,
-  30,
-  31
-];
+export default (
+  leapYear: boolean
+): [
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number
+] => [31, leapYear ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
diff --git a/date/daysInYear.json b/date/daysInYear.json
index 601818cc..0d97c09a 100644
--- a/date/daysInYear.json
+++ b/date/daysInYear.json
@@ -1,7 +1,7 @@
 {
   "name": "daysInYear",
   "description": "TODO: Fill short description here.",
-  "signature": "(year: any) => number",
+  "signature": "(year: number) => number",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/daysInYear.md b/date/daysInYear.md
index 03de6148..a6f167df 100644
--- a/date/daysInYear.md
+++ b/date/daysInYear.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(year: any) => number
+(year: number) => number
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/daysInYear.ts b/date/daysInYear.ts
index 13c489da..4a364b99 100644
--- a/date/daysInYear.ts
+++ b/date/daysInYear.ts
@@ -2,4 +2,4 @@ import sum from "../array/sum";
 import daysInMonths from "./daysInMonths";
 import leapYear from "./leapYear";
 
-export default year => sum(daysInMonths(leapYear(year)));
+export default (year: number) => sum(daysInMonths(leapYear(year)));
diff --git a/date/displayMonth.json b/date/displayMonth.json
index f033d622..95707c1c 100644
--- a/date/displayMonth.json
+++ b/date/displayMonth.json
@@ -1,7 +1,7 @@
 {
   "name": "displayMonth",
   "description": "TODO: Fill short description here.",
-  "signature": "(monthIndex: any) => string",
+  "signature": "(monthIndex: number) => string",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/displayMonth.md b/date/displayMonth.md
index 23bb48d2..71e29976 100644
--- a/date/displayMonth.md
+++ b/date/displayMonth.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(monthIndex: any) => string
+(monthIndex: number) => string
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/displayMonth.ts b/date/displayMonth.ts
index 83a1e0b6..29e50e5b 100644
--- a/date/displayMonth.ts
+++ b/date/displayMonth.ts
@@ -1,3 +1,3 @@
 import monthNames from "./monthNames";
 
-export default monthIndex => monthNames[monthIndex % 12];
+export default (monthIndex: number) => monthNames[monthIndex % 12];
diff --git a/date/displayTime.json b/date/displayTime.json
index c73d4c32..837310bf 100644
--- a/date/displayTime.json
+++ b/date/displayTime.json
@@ -1,7 +1,7 @@
 {
   "name": "displayTime",
   "description": "TODO: Fill short description here.",
-  "signature": "(source: any, showSeconds: any) => string",
+  "signature": "(\n  source: [number, number, number],\n  showSeconds: boolean\n) => string",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/displayTime.md b/date/displayTime.md
index e02d2a67..3ae4381c 100644
--- a/date/displayTime.md
+++ b/date/displayTime.md
@@ -4,6 +4,9 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(source: any, showSeconds: any) => string
+(
+  source: [number, number, number],
+  showSeconds: boolean
+) => string
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/displayTime.ts b/date/displayTime.ts
index fc78bc18..b1bfe6fc 100644
--- a/date/displayTime.ts
+++ b/date/displayTime.ts
@@ -1,4 +1,4 @@
-export default (source, showSeconds) => {
+export default (source: [number, number, number], showSeconds: boolean) => {
   const [hours, minutes, seconds] = source.map(_ => _ + "");
 
   const padded = [
diff --git a/date/endOfDay.json b/date/endOfDay.json
index 47e30618..0458a645 100644
--- a/date/endOfDay.json
+++ b/date/endOfDay.json
@@ -1,7 +1,7 @@
 {
   "name": "endOfDay",
   "description": "TODO: Fill short description here.",
-  "signature": "(\n  date: any,\n  timezoneOffset?: number,\n  local?: boolean\n) => Date",
+  "signature": "(\n  date: string | number | Date,\n  timezoneOffset?: number,\n  local?: boolean\n) => Date",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/endOfDay.md b/date/endOfDay.md
index 15f9a5fe..8ba2cda9 100644
--- a/date/endOfDay.md
+++ b/date/endOfDay.md
@@ -5,7 +5,7 @@
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  date: any,
+  date: string | number | Date,
   timezoneOffset?: number,
   local?: boolean
 ) => Date
diff --git a/date/endOfDay.ts b/date/endOfDay.ts
index 71f92a0f..546a0024 100644
--- a/date/endOfDay.ts
+++ b/date/endOfDay.ts
@@ -1,6 +1,10 @@
 import toLocalDateTime from "./toLocalDateTime";
 
-export default (date, timezoneOffset = 0, local = true) => {
+export default (
+  date: string | number | Date,
+  timezoneOffset = 0,
+  local = true
+) => {
   const newDate = new Date(date);
   newDate.setHours(24, 0, 0, 0);
 
diff --git a/date/formatDate.json b/date/formatDate.json
index 2ba85e7e..e15a49e6 100644
--- a/date/formatDate.json
+++ b/date/formatDate.json
@@ -1,7 +1,7 @@
 {
   "name": "formatDate",
   "description": "TODO: Fill short description here.",
-  "signature": "(sourceDate: any, timezoneOffset?: number) => string",
+  "signature": "(sourceDate: Date, timezoneOffset?: number) => string",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/formatDate.md b/date/formatDate.md
index 00d03f08..3227aad4 100644
--- a/date/formatDate.md
+++ b/date/formatDate.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(sourceDate: any, timezoneOffset?: number) => string
+(sourceDate: Date, timezoneOffset?: number) => string
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/formatDate.ts b/date/formatDate.ts
index f6fcac30..50bd88b1 100644
--- a/date/formatDate.ts
+++ b/date/formatDate.ts
@@ -1,6 +1,6 @@
 import toLocalDateTime from "./toLocalDateTime";
 
-export default (sourceDate, timezoneOffset = 0) => {
+export default (sourceDate: Date, timezoneOffset: number = 0) => {
   const localDate = toLocalDateTime(sourceDate, timezoneOffset);
 
   const [m, a, y] = [
diff --git a/date/formatDateTime.json b/date/formatDateTime.json
index 9c6bde48..69a087ec 100644
--- a/date/formatDateTime.json
+++ b/date/formatDateTime.json
@@ -1,7 +1,7 @@
 {
   "name": "formatDateTime",
   "description": "TODO: Fill short description here.",
-  "signature": "(\n  sourceDate: any,\n  showSeconds?: boolean,\n  timezoneOffset?: number\n) => string",
+  "signature": "(\n  sourceDate: Date,\n  showSeconds?: boolean,\n  timezoneOffset?: number\n) => string",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/formatDateTime.md b/date/formatDateTime.md
index 572aeb24..69eae52e 100644
--- a/date/formatDateTime.md
+++ b/date/formatDateTime.md
@@ -5,7 +5,7 @@
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  sourceDate: any,
+  sourceDate: Date,
   showSeconds?: boolean,
   timezoneOffset?: number
 ) => string
diff --git a/date/formatDateTime.ts b/date/formatDateTime.ts
index a350c841..94cd878c 100644
--- a/date/formatDateTime.ts
+++ b/date/formatDateTime.ts
@@ -1,7 +1,7 @@
 import formatDate from "./formatDate";
 import formatTime from "./formatTime";
 
-export default (sourceDate, showSeconds = false, timezoneOffset = 0) => {
+export default (sourceDate: Date, showSeconds = false, timezoneOffset = 0) => {
   const date = formatDate(sourceDate, timezoneOffset);
   const time = formatTime(sourceDate, showSeconds, timezoneOffset);
 
diff --git a/date/formatDisplayDate.json b/date/formatDisplayDate.json
index 3e1f8d4c..145194da 100644
--- a/date/formatDisplayDate.json
+++ b/date/formatDisplayDate.json
@@ -1,7 +1,7 @@
 {
   "name": "formatDisplayDate",
   "description": "TODO: Fill short description here.",
-  "signature": "(\n  sourceDate: any,\n  showDay?: boolean,\n  timezoneOffset?: number\n) => string",
+  "signature": "(\n  sourceDate: Date,\n  showDay?: boolean,\n  timezoneOffset?: number\n) => string",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/formatDisplayDate.md b/date/formatDisplayDate.md
index 52deddcd..dd9dd814 100644
--- a/date/formatDisplayDate.md
+++ b/date/formatDisplayDate.md
@@ -5,7 +5,7 @@
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  sourceDate: any,
+  sourceDate: Date,
   showDay?: boolean,
   timezoneOffset?: number
 ) => string
diff --git a/date/formatDisplayDate.ts b/date/formatDisplayDate.ts
index 70eddb0c..38fb8ab9 100644
--- a/date/formatDisplayDate.ts
+++ b/date/formatDisplayDate.ts
@@ -1,7 +1,7 @@
 import toLocalDateTime from "./toLocalDateTime";
 import displayMonth from "./displayMonth";
 
-export default (sourceDate, showDay = false, timezoneOffset = 0) => {
+export default (sourceDate: Date, showDay = false, timezoneOffset = 0) => {
   const localDate = toLocalDateTime(sourceDate, timezoneOffset);
   const day = localDate.getDate();
   const monthIndex = localDate.getMonth();
diff --git a/date/formatDuration.json b/date/formatDuration.json
index 108d59f6..18c116f0 100644
--- a/date/formatDuration.json
+++ b/date/formatDuration.json
@@ -1,7 +1,7 @@
 {
   "name": "formatDuration",
   "description": "TODO: Fill short description here.",
-  "signature": "(duration: any, showSeconds?: boolean) => string",
+  "signature": "(duration: number, showSeconds?: boolean) => string",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/formatDuration.md b/date/formatDuration.md
index 3dead43e..5a59ebe8 100644
--- a/date/formatDuration.md
+++ b/date/formatDuration.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(duration: any, showSeconds?: boolean) => string
+(duration: number, showSeconds?: boolean) => string
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/formatDuration.ts b/date/formatDuration.ts
index bda1bc18..9401437c 100644
--- a/date/formatDuration.ts
+++ b/date/formatDuration.ts
@@ -5,7 +5,7 @@ import toMinutes from "./toMinutes";
 import toSeconds from "./toSeconds";
 import displayTime from "./displayTime";
 
-export default (duration, showSeconds = false) => {
+export default (duration: number, showSeconds = false) => {
   const hours = Math.floor(toHours(duration));
   const minutes = Math.floor(toMinutes(duration - fromHours(hours)));
 
diff --git a/date/formatTime.js b/date/formatTime.js
index 6c01768f..1cb569ae 100644
--- a/date/formatTime.js
+++ b/date/formatTime.js
@@ -4,11 +4,11 @@ import displayTime from "./displayTime.js";
 export default (sourceDate, showSeconds = false, timezoneOffset = 0) => {
   const localDate = toLocalDateTime(sourceDate, timezoneOffset);
 
-  const source = [
+  const [hours, minutes, seconds] = [
     localDate.getUTCHours(),
     localDate.getUTCMinutes(),
     localDate.getUTCSeconds()
   ];
 
-  return displayTime(source, showSeconds);
+  return displayTime([hours, minutes, seconds], showSeconds);
 };
diff --git a/date/formatTime.json b/date/formatTime.json
index a2391390..e918ede6 100644
--- a/date/formatTime.json
+++ b/date/formatTime.json
@@ -1,7 +1,7 @@
 {
   "name": "formatTime",
   "description": "TODO: Fill short description here.",
-  "signature": "(\n  sourceDate: any,\n  showSeconds?: boolean,\n  timezoneOffset?: number\n) => string",
+  "signature": "(\n  sourceDate: Date,\n  showSeconds?: boolean,\n  timezoneOffset?: number\n) => string",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/formatTime.md b/date/formatTime.md
index e496b1e7..92ee6ff9 100644
--- a/date/formatTime.md
+++ b/date/formatTime.md
@@ -5,7 +5,7 @@
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  sourceDate: any,
+  sourceDate: Date,
   showSeconds?: boolean,
   timezoneOffset?: number
 ) => string
diff --git a/date/formatTime.ts b/date/formatTime.ts
index 26e55f00..e657b22a 100644
--- a/date/formatTime.ts
+++ b/date/formatTime.ts
@@ -1,14 +1,14 @@
 import toLocalDateTime from "./toLocalDateTime";
 import displayTime from "./displayTime";
 
-export default (sourceDate, showSeconds = false, timezoneOffset = 0) => {
+export default (sourceDate: Date, showSeconds = false, timezoneOffset = 0) => {
   const localDate = toLocalDateTime(sourceDate, timezoneOffset);
 
-  const source = [
+  const [hours, minutes, seconds] = [
     localDate.getUTCHours(),
     localDate.getUTCMinutes(),
     localDate.getUTCSeconds()
   ];
 
-  return displayTime(source, showSeconds);
+  return displayTime([hours, minutes, seconds], showSeconds);
 };
diff --git a/date/fromDays.json b/date/fromDays.json
index de6eab7b..22b866f5 100644
--- a/date/fromDays.json
+++ b/date/fromDays.json
@@ -1,7 +1,7 @@
 {
   "name": "fromDays",
   "description": "TODO: Fill short description here.",
-  "signature": "(days: any) => number",
+  "signature": "(days: number) => number",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/fromDays.md b/date/fromDays.md
index 588ae71c..cc963c98 100644
--- a/date/fromDays.md
+++ b/date/fromDays.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(days: any) => number
+(days: number) => number
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/fromDays.ts b/date/fromDays.ts
index ea8d490e..a30ed404 100644
--- a/date/fromDays.ts
+++ b/date/fromDays.ts
@@ -1,3 +1,3 @@
 import fromHours from "./fromHours";
 
-export default days => fromHours(days * 24);
+export default (days: number) => fromHours(days * 24);
diff --git a/date/fromHours.json b/date/fromHours.json
index 65034044..c04a6a8c 100644
--- a/date/fromHours.json
+++ b/date/fromHours.json
@@ -1,7 +1,7 @@
 {
   "name": "fromHours",
   "description": "TODO: Fill short description here.",
-  "signature": "(hours: any) => number",
+  "signature": "(hours: number) => number",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/fromHours.md b/date/fromHours.md
index ded6d442..a8b3f21f 100644
--- a/date/fromHours.md
+++ b/date/fromHours.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(hours: any) => number
+(hours: number) => number
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/fromHours.ts b/date/fromHours.ts
index 6a5f9617..58d75a47 100644
--- a/date/fromHours.ts
+++ b/date/fromHours.ts
@@ -1,3 +1,3 @@
 import fromMinutes from "./fromMinutes";
 
-export default hours => fromMinutes(hours * 60);
+export default (hours: number) => fromMinutes(hours * 60);
diff --git a/date/fromMinutes.json b/date/fromMinutes.json
index 986a93ee..ac3e6e8c 100644
--- a/date/fromMinutes.json
+++ b/date/fromMinutes.json
@@ -1,7 +1,7 @@
 {
   "name": "fromMinutes",
   "description": "TODO: Fill short description here.",
-  "signature": "(minutes: any) => number",
+  "signature": "(minutes: number) => number",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/fromMinutes.md b/date/fromMinutes.md
index 41238e7e..c095e696 100644
--- a/date/fromMinutes.md
+++ b/date/fromMinutes.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(minutes: any) => number
+(minutes: number) => number
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/fromMinutes.ts b/date/fromMinutes.ts
index 6e32741a..26e5d2ec 100644
--- a/date/fromMinutes.ts
+++ b/date/fromMinutes.ts
@@ -1,3 +1,3 @@
 import fromSeconds from "./fromSeconds";
 
-export default minutes => fromSeconds(minutes * 60);
+export default (minutes: number) => fromSeconds(minutes * 60);
diff --git a/date/fromSeconds.json b/date/fromSeconds.json
index ef4d3ada..12343565 100644
--- a/date/fromSeconds.json
+++ b/date/fromSeconds.json
@@ -1,7 +1,7 @@
 {
   "name": "fromSeconds",
   "description": "TODO: Fill short description here.",
-  "signature": "(seconds: any) => number",
+  "signature": "(seconds: number) => number",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/fromSeconds.md b/date/fromSeconds.md
index 2f674d1d..1da52d80 100644
--- a/date/fromSeconds.md
+++ b/date/fromSeconds.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(seconds: any) => number
+(seconds: number) => number
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/fromSeconds.ts b/date/fromSeconds.ts
index c0770d78..f19d1e92 100644
--- a/date/fromSeconds.ts
+++ b/date/fromSeconds.ts
@@ -1 +1 @@
-export default seconds => seconds * 1000;
+export default (seconds: number) => seconds * 1000;
diff --git a/date/joinDateTime.json b/date/joinDateTime.json
index e0ab224e..1c4641a3 100644
--- a/date/joinDateTime.json
+++ b/date/joinDateTime.json
@@ -1,7 +1,7 @@
 {
   "name": "joinDateTime",
   "description": "TODO: Fill short description here.",
-  "signature": "(...xs: any[]) => string",
+  "signature": "(...xs: string[]) => string",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/joinDateTime.md b/date/joinDateTime.md
index 4075dc00..de8bd7a6 100644
--- a/date/joinDateTime.md
+++ b/date/joinDateTime.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(...xs: any[]) => string
+(...xs: string[]) => string
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/joinDateTime.ts b/date/joinDateTime.ts
index 328ef7c9..23c1b067 100644
--- a/date/joinDateTime.ts
+++ b/date/joinDateTime.ts
@@ -1 +1 @@
-export default (...xs) => xs.join("T");
+export default (...xs: string[]) => xs.join("T");
diff --git a/date/leapYear.json b/date/leapYear.json
index 72cbaea0..55c89670 100644
--- a/date/leapYear.json
+++ b/date/leapYear.json
@@ -1,7 +1,7 @@
 {
   "name": "leapYear",
   "description": "TODO: Fill short description here.",
-  "signature": "(year: any) => boolean",
+  "signature": "(year: number) => boolean",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/leapYear.md b/date/leapYear.md
index d36cc719..6c5b9c9c 100644
--- a/date/leapYear.md
+++ b/date/leapYear.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(year: any) => boolean
+(year: number) => boolean
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/leapYear.ts b/date/leapYear.ts
index 62ab3314..9009ddcd 100644
--- a/date/leapYear.ts
+++ b/date/leapYear.ts
@@ -1 +1 @@
-export default year => new Date(year, 1, 29).getMonth() === 1;
+export default (year: number) => new Date(year, 1, 29).getMonth() === 1;
diff --git a/date/offsetByBit.js b/date/offsetByBit.js
index 7581ee97..07a6a757 100644
--- a/date/offsetByBit.js
+++ b/date/offsetByBit.js
@@ -2,4 +2,4 @@ import fromSeconds from "./fromSeconds.js";
 
 const SECOND = fromSeconds(1);
 
-export default date => new Date(date - SECOND);
+export default date => new Date(date.valueOf() - SECOND);
diff --git a/date/offsetByBit.json b/date/offsetByBit.json
index b88fa0ba..5fd24cad 100644
--- a/date/offsetByBit.json
+++ b/date/offsetByBit.json
@@ -1,7 +1,7 @@
 {
   "name": "offsetByBit",
   "description": "TODO: Fill short description here.",
-  "signature": "(date: any) => Date",
+  "signature": "(date: number | Date) => Date",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/offsetByBit.md b/date/offsetByBit.md
index 0ad50b67..a06f446d 100644
--- a/date/offsetByBit.md
+++ b/date/offsetByBit.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(date: any) => Date
+(date: number | Date) => Date
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/offsetByBit.ts b/date/offsetByBit.ts
index 6df9dd14..0fb12447 100644
--- a/date/offsetByBit.ts
+++ b/date/offsetByBit.ts
@@ -2,4 +2,4 @@ import fromSeconds from "./fromSeconds";
 
 const SECOND = fromSeconds(1);
 
-export default date => new Date(date - SECOND);
+export default (date: Date | number) => new Date(date.valueOf() - SECOND);
diff --git a/date/splitDateTime.json b/date/splitDateTime.json
index ae00daa1..8ac0b4f2 100644
--- a/date/splitDateTime.json
+++ b/date/splitDateTime.json
@@ -1,7 +1,7 @@
 {
   "name": "splitDateTime",
   "description": "TODO: Fill short description here.",
-  "signature": "(dateTimeString: any) => any",
+  "signature": "(dateTimeString: string) => string[]",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/splitDateTime.md b/date/splitDateTime.md
index 8fc84f93..c3d271cf 100644
--- a/date/splitDateTime.md
+++ b/date/splitDateTime.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(dateTimeString: any) => any
+(dateTimeString: string) => string[]
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/splitDateTime.ts b/date/splitDateTime.ts
index 0b871afb..f781a075 100644
--- a/date/splitDateTime.ts
+++ b/date/splitDateTime.ts
@@ -1 +1 @@
-export default dateTimeString => dateTimeString.split("T");
+export default (dateTimeString: string) => dateTimeString.split("T");
diff --git a/date/startOfDay.json b/date/startOfDay.json
index 51703226..d37e783c 100644
--- a/date/startOfDay.json
+++ b/date/startOfDay.json
@@ -1,7 +1,7 @@
 {
   "name": "startOfDay",
   "description": "TODO: Fill short description here.",
-  "signature": "(\n  date: any,\n  timezoneOffset?: number,\n  local?: boolean\n) => Date",
+  "signature": "(\n  date: string | number | Date,\n  timezoneOffset?: number,\n  local?: boolean\n) => Date",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/startOfDay.md b/date/startOfDay.md
index 22e28d4a..43f4f558 100644
--- a/date/startOfDay.md
+++ b/date/startOfDay.md
@@ -5,7 +5,7 @@
 <!-- prettier-ignore-start -->
 ```typescript
 (
-  date: any,
+  date: string | number | Date,
   timezoneOffset?: number,
   local?: boolean
 ) => Date
diff --git a/date/startOfDay.ts b/date/startOfDay.ts
index 82289a4b..c32f86d5 100644
--- a/date/startOfDay.ts
+++ b/date/startOfDay.ts
@@ -1,6 +1,10 @@
 import toLocalDateTime from "./toLocalDateTime";
 
-export default (date, timezoneOffset = 0, local = true) => {
+export default (
+  date: string | number | Date,
+  timezoneOffset = 0,
+  local = true
+) => {
   const newDate = new Date(date);
   newDate.setHours(0, 0, 0, 0);
 
diff --git a/date/subtractDays.json b/date/subtractDays.json
index 51bec5c9..fb15ab8f 100644
--- a/date/subtractDays.json
+++ b/date/subtractDays.json
@@ -1,7 +1,7 @@
 {
   "name": "subtractDays",
   "description": "TODO: Fill short description here.",
-  "signature": "(sourceDate: any, numberOfDays: any) => Date",
+  "signature": "(\n  sourceDate: string | number | Date,\n  numberOfDays: number\n) => Date",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/subtractDays.md b/date/subtractDays.md
index 3e2d05d0..51f6ab60 100644
--- a/date/subtractDays.md
+++ b/date/subtractDays.md
@@ -4,6 +4,9 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(sourceDate: any, numberOfDays: any) => Date
+(
+  sourceDate: string | number | Date,
+  numberOfDays: number
+) => Date
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/subtractDays.ts b/date/subtractDays.ts
index 3dbbb505..0efa06f3 100644
--- a/date/subtractDays.ts
+++ b/date/subtractDays.ts
@@ -1,4 +1,4 @@
-export default (sourceDate, numberOfDays) => {
+export default (sourceDate: string | number | Date, numberOfDays: number) => {
   const date = new Date(sourceDate);
 
   date.setDate(date.getDate() - numberOfDays);
diff --git a/date/toDate.json b/date/toDate.json
index 6b36007d..59a70d33 100644
--- a/date/toDate.json
+++ b/date/toDate.json
@@ -1,7 +1,7 @@
 {
   "name": "toDate",
   "description": "TODO: Fill short description here.",
-  "signature": "(date: any) => string",
+  "signature": "(date: Date) => string",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/toDate.md b/date/toDate.md
index 64346443..f0d05cc7 100644
--- a/date/toDate.md
+++ b/date/toDate.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(date: any) => string
+(date: Date) => string
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/toDate.ts b/date/toDate.ts
index 04b7bb21..987c7e9c 100644
--- a/date/toDate.ts
+++ b/date/toDate.ts
@@ -1,4 +1,4 @@
-export default date => {
+export default (date: Date) => {
   const day = date.getDate();
   const month = date.getMonth() + 1;
   const year = date.getFullYear();
diff --git a/date/toDates.json b/date/toDates.json
index 1e8459a0..d2382d71 100644
--- a/date/toDates.json
+++ b/date/toDates.json
@@ -1,7 +1,7 @@
 {
   "name": "toDates",
   "description": "TODO: Fill short description here.",
-  "signature": "(xs: any) => any",
+  "signature": "(xs: (string | number | Date)[]) => Date[]",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/toDates.md b/date/toDates.md
index 225de78f..2464a4b6 100644
--- a/date/toDates.md
+++ b/date/toDates.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(xs: any) => any
+(xs: (string | number | Date)[]) => Date[]
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/toDates.ts b/date/toDates.ts
index 8fb2e180..6490b81b 100644
--- a/date/toDates.ts
+++ b/date/toDates.ts
@@ -1 +1 @@
-export default xs => xs.map(x => new Date(x));
+export default (xs: (string | number | Date)[]) => xs.map(x => new Date(x));
diff --git a/date/toDays.json b/date/toDays.json
index 57e70b9e..f8fb1d70 100644
--- a/date/toDays.json
+++ b/date/toDays.json
@@ -1,7 +1,7 @@
 {
   "name": "toDays",
   "description": "TODO: Fill short description here.",
-  "signature": "(milliseconds: any) => number",
+  "signature": "(milliseconds: number) => number",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/toDays.md b/date/toDays.md
index b748b5f9..984bdaa4 100644
--- a/date/toDays.md
+++ b/date/toDays.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(milliseconds: any) => number
+(milliseconds: number) => number
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/toDays.ts b/date/toDays.ts
index 1d9e7132..cffed990 100644
--- a/date/toDays.ts
+++ b/date/toDays.ts
@@ -1,3 +1,3 @@
 import toHours from "./toHours";
 
-export default milliseconds => toHours(milliseconds) / 24;
+export default (milliseconds: number) => toHours(milliseconds) / 24;
diff --git a/date/toHours.json b/date/toHours.json
index 7d2eb044..18ccfee2 100644
--- a/date/toHours.json
+++ b/date/toHours.json
@@ -1,7 +1,7 @@
 {
   "name": "toHours",
   "description": "TODO: Fill short description here.",
-  "signature": "(milliseconds: any) => number",
+  "signature": "(milliseconds: number) => number",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/toHours.md b/date/toHours.md
index 1ed852a6..91bbc2b2 100644
--- a/date/toHours.md
+++ b/date/toHours.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(milliseconds: any) => number
+(milliseconds: number) => number
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/toHours.ts b/date/toHours.ts
index 44509b4b..bec1f273 100644
--- a/date/toHours.ts
+++ b/date/toHours.ts
@@ -1,3 +1,3 @@
 import toMinutes from "./toMinutes";
 
-export default milliseconds => toMinutes(milliseconds) / 60;
+export default (milliseconds: number) => toMinutes(milliseconds) / 60;
diff --git a/date/toISO.json b/date/toISO.json
index d2792866..231ca90f 100644
--- a/date/toISO.json
+++ b/date/toISO.json
@@ -1,7 +1,7 @@
 {
   "name": "toISO",
   "description": "TODO: Fill short description here.",
-  "signature": "(x: any) => any",
+  "signature": "(x: Date) => string",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/toISO.md b/date/toISO.md
index 12d68ca9..49e8839c 100644
--- a/date/toISO.md
+++ b/date/toISO.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(x: any) => any
+(x: Date) => string
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/toISO.ts b/date/toISO.ts
index 9ac56e00..12d68a84 100644
--- a/date/toISO.ts
+++ b/date/toISO.ts
@@ -1 +1 @@
-export default x => x.toISOString();
+export default (x: Date) => x.toISOString();
diff --git a/date/toISOFromLocalDateTime.json b/date/toISOFromLocalDateTime.json
index 671c7b32..b06b6374 100644
--- a/date/toISOFromLocalDateTime.json
+++ b/date/toISOFromLocalDateTime.json
@@ -1,7 +1,7 @@
 {
   "name": "toISOFromLocalDateTime",
   "description": "TODO: Fill short description here.",
-  "signature": "(date: any) => string",
+  "signature": "(date: Date) => string",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/toISOFromLocalDateTime.md b/date/toISOFromLocalDateTime.md
index 20392bf2..7310db3c 100644
--- a/date/toISOFromLocalDateTime.md
+++ b/date/toISOFromLocalDateTime.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(date: any) => string
+(date: Date) => string
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/toISOFromLocalDateTime.ts b/date/toISOFromLocalDateTime.ts
index f4d527df..e3d6016f 100644
--- a/date/toISOFromLocalDateTime.ts
+++ b/date/toISOFromLocalDateTime.ts
@@ -1,6 +1,6 @@
 import fromMinutes from "./fromMinutes";
 
-export default date =>
+export default (date: Date) =>
   new Date(
     date.valueOf() - fromMinutes(date.getTimezoneOffset())
   ).toISOString();
diff --git a/date/toLocalDateTime.json b/date/toLocalDateTime.json
index a3f43527..a935be42 100644
--- a/date/toLocalDateTime.json
+++ b/date/toLocalDateTime.json
@@ -1,7 +1,7 @@
 {
   "name": "toLocalDateTime",
   "description": "TODO: Fill short description here.",
-  "signature": "(date: any, timezoneOffset?: number) => Date",
+  "signature": "(date: Date, timezoneOffset?: number) => Date",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/toLocalDateTime.md b/date/toLocalDateTime.md
index a9c058c5..679d4a20 100644
--- a/date/toLocalDateTime.md
+++ b/date/toLocalDateTime.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(date: any, timezoneOffset?: number) => Date
+(date: Date, timezoneOffset?: number) => Date
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/toLocalDateTime.ts b/date/toLocalDateTime.ts
index c739d259..7d84958d 100644
--- a/date/toLocalDateTime.ts
+++ b/date/toLocalDateTime.ts
@@ -1,4 +1,4 @@
 import fromMinutes from "./fromMinutes";
 
-export default (date, timezoneOffset = 0) =>
+export default (date: Date, timezoneOffset: number = 0) =>
   new Date(date.valueOf() - fromMinutes(timezoneOffset));
diff --git a/date/toMinutes.json b/date/toMinutes.json
index a7ecfa08..1bfb4fae 100644
--- a/date/toMinutes.json
+++ b/date/toMinutes.json
@@ -1,7 +1,7 @@
 {
   "name": "toMinutes",
   "description": "TODO: Fill short description here.",
-  "signature": "(milliseconds: any) => number",
+  "signature": "(milliseconds: number) => number",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/toMinutes.md b/date/toMinutes.md
index 74e2fc17..405f5c85 100644
--- a/date/toMinutes.md
+++ b/date/toMinutes.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(milliseconds: any) => number
+(milliseconds: number) => number
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/toMinutes.ts b/date/toMinutes.ts
index 3ef8dcca..fd8f8a28 100644
--- a/date/toMinutes.ts
+++ b/date/toMinutes.ts
@@ -1,3 +1,3 @@
 import toSeconds from "./toSeconds";
 
-export default milliseconds => toSeconds(milliseconds) / 60;
+export default (milliseconds: number) => toSeconds(milliseconds) / 60;
diff --git a/date/toSeconds.json b/date/toSeconds.json
index bfd03aab..db6b3fc5 100644
--- a/date/toSeconds.json
+++ b/date/toSeconds.json
@@ -1,7 +1,7 @@
 {
   "name": "toSeconds",
   "description": "TODO: Fill short description here.",
-  "signature": "(milliseconds: any) => number",
+  "signature": "(milliseconds: number) => number",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/toSeconds.md b/date/toSeconds.md
index e1adfbcf..003f9fd7 100644
--- a/date/toSeconds.md
+++ b/date/toSeconds.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(milliseconds: any) => number
+(milliseconds: number) => number
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/toSeconds.ts b/date/toSeconds.ts
index 39f86994..eca6e443 100644
--- a/date/toSeconds.ts
+++ b/date/toSeconds.ts
@@ -1 +1 @@
-export default milliseconds => milliseconds / 1000;
+export default (milliseconds: number) => milliseconds / 1000;
diff --git a/date/valid.js b/date/valid.js
index 83119e28..1e1ee749 100644
--- a/date/valid.js
+++ b/date/valid.js
@@ -1 +1 @@
-export default date => date && date instanceof Date;
+export default date => (date ? date instanceof Date : false);
diff --git a/date/valid.json b/date/valid.json
index f7e19c9e..314fe758 100644
--- a/date/valid.json
+++ b/date/valid.json
@@ -1,7 +1,7 @@
 {
   "name": "valid",
   "description": "TODO: Fill short description here.",
-  "signature": "(date: any) => boolean",
+  "signature": "(date?: any) => boolean",
   "examples": [
     {
       "language": "javascript",
diff --git a/date/valid.md b/date/valid.md
index e2bfbf14..014ebdd5 100644
--- a/date/valid.md
+++ b/date/valid.md
@@ -4,6 +4,6 @@
 
 <!-- prettier-ignore-start -->
 ```typescript
-(date: any) => boolean
+(date?: any) => boolean
 ```
 <!-- prettier-ignore-end -->
diff --git a/date/valid.ts b/date/valid.ts
index 83119e28..0f82e166 100644
--- a/date/valid.ts
+++ b/date/valid.ts
@@ -1 +1 @@
-export default date => date && date instanceof Date;
+export default (date?: any): boolean => (date ? date instanceof Date : false);
diff --git a/debug/README.md b/debug/README.md
index aba589e5..70607335 100644
--- a/debug/README.md
+++ b/debug/README.md
@@ -21,6 +21,13 @@ Computes a difference between two objects.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(obj1: object, obj2: object) => object
+(
+  obj1?: {
+    [index: string]: any;
+  },
+  obj2?: {
+    [index: string]: any;
+  }
+) => object
 ```
 <!-- prettier-ignore-end -->
diff --git a/debug/assert.ts b/debug/assert.ts
index 5638c800..ef948a26 100644
--- a/debug/assert.ts
+++ b/debug/assert.ts
@@ -22,7 +22,7 @@ const assert = (
   }
 };
 
-export const throws = (f: () => void): Error => {
+export const throws = (f: () => void): Error | undefined => {
   try {
     f();
 
diff --git a/debug/diff.js b/debug/diff.js
index a87f7a81..cbd5d75e 100644
--- a/debug/diff.js
+++ b/debug/diff.js
@@ -41,7 +41,7 @@ const compareValues = (value1, value2) => {
 };
 
 const diff = (obj1, obj2) => {
-  if (isValue(obj1) || isValue(obj2)) {
+  if (!obj1 || !obj2 || isValue(obj1) || isValue(obj2)) {
     const comparisonResult = compareValues(obj1, obj2);
 
     return comparisonResult !== VALUE_UNCHANGED
@@ -49,31 +49,31 @@ const diff = (obj1, obj2) => {
           type: comparisonResult,
           data: [obj1, obj2]
         }
-      : null;
+      : {};
   }
 
   const result = {};
 
   for (const key in obj1) {
-    if (isFunction(obj1[key])) {
-      continue;
-    }
-
-    let value2 = undefined;
+    const value1 = obj1[key];
 
-    if (isDefined(obj2[key])) {
-      value2 = obj2[key];
+    if (isFunction(value1)) {
+      continue;
     }
 
-    result[key] = diff(obj1[key], value2);
+    const value2 = obj2[key];
+    result[key] = diff(value1, value2);
   }
 
   for (const key in obj2) {
-    if (isFunction(obj2[key]) || isDefined(result[key])) {
+    const value2 = obj2[key];
+    const existingValue = result[key];
+
+    if (isFunction(value2) || isDefined(existingValue)) {
       continue;
     }
 
-    result[key] = diff(undefined, obj2[key]);
+    result[key] = diff(undefined, value2);
   }
 
   return filter(
diff --git a/debug/diff.json b/debug/diff.json
index 471e1e00..3047f61b 100644
--- a/debug/diff.json
+++ b/debug/diff.json
@@ -1,7 +1,7 @@
 {
   "name": "diff",
   "description": "Computes a difference between two objects.",
-  "signature": "(obj1: object, obj2: object) => object",
+  "signature": "(\n  obj1?: {\n    [index: string]: any;\n  },\n  obj2?: {\n    [index: string]: any;\n  }\n) => object",
   "examples": [
     {
       "language": "javascript",
diff --git a/debug/diff.md b/debug/diff.md
index ea57e1b3..a0d09d5f 100644
--- a/debug/diff.md
+++ b/debug/diff.md
@@ -6,6 +6,13 @@ Computes a difference between two objects.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(obj1: object, obj2: object) => object
+(
+  obj1?: {
+    [index: string]: any;
+  },
+  obj2?: {
+    [index: string]: any;
+  }
+) => object
 ```
 <!-- prettier-ignore-end -->
diff --git a/debug/diff.test.ts b/debug/diff.test.ts
index 8c62528c..83a9f278 100644
--- a/debug/diff.test.ts
+++ b/debug/diff.test.ts
@@ -77,4 +77,11 @@ describe("diff", () => {
       a: { data: [1, 5], type: VALUE_UPDATED }
     });
   });
+
+  it("detects object deletions", () => {
+    expect(diff({ a: 1 }, undefined)).toEqual({
+      data: [{ a: 1 }, undefined],
+      type: VALUE_DELETED
+    });
+  });
 });
diff --git a/debug/diff.ts b/debug/diff.ts
index 4061dada..a560f2fe 100644
--- a/debug/diff.ts
+++ b/debug/diff.ts
@@ -40,8 +40,11 @@ const compareValues = (value1: any, value2: any) => {
   return VALUE_UPDATED;
 };
 
-const diff = (obj1: object, obj2: object) => {
-  if (isValue(obj1) || isValue(obj2)) {
+const diff = (
+  obj1?: { [index: string]: any },
+  obj2?: { [index: string]: any }
+): object => {
+  if (!obj1 || !obj2 || isValue(obj1) || isValue(obj2)) {
     const comparisonResult = compareValues(obj1, obj2);
 
     return comparisonResult !== VALUE_UNCHANGED
@@ -49,31 +52,33 @@ const diff = (obj1: object, obj2: object) => {
           type: comparisonResult,
           data: [obj1, obj2]
         }
-      : null;
+      : {};
   }
 
-  const result = {};
+  const result: { [index: string]: any } = {};
 
   for (const key in obj1) {
-    if (isFunction(obj1[key])) {
+    const value1 = obj1[key];
+
+    if (isFunction(value1)) {
       continue;
     }
 
-    let value2 = undefined;
-
-    if (isDefined(obj2[key])) {
-      value2 = obj2[key];
-    }
+    const value2 = obj2[key];
 
-    result[key] = diff(obj1[key], value2);
+    result[key] = diff(value1, value2);
   }
 
   for (const key in obj2) {
-    if (isFunction(obj2[key]) || isDefined(result[key])) {
+    const value2 = obj2[key];
+
+    const existingValue = result[key];
+
+    if (isFunction(value2) || isDefined(existingValue)) {
       continue;
     }
 
-    result[key] = diff(undefined, obj2[key]);
+    result[key] = diff(undefined, value2);
   }
 
   return filter(
diff --git a/encoding/README.md b/encoding/README.md
index 08026f4b..78bb2f76 100644
--- a/encoding/README.md
+++ b/encoding/README.md
@@ -7,15 +7,7 @@ Provides a way to encode strings and bytes from and into Base64URL.
 <!-- prettier-ignore-start -->
 ```typescript
 {
-  decode: (
-    text: string,
-    context?: {
-      atob: (byteString: string) => string;
-      TextDecoder: new (encoding: string) => {
-        decode: (input?: Uint8Array) => string;
-      };
-    }
-  ) => string;
+  decode: (text: string, context?: DecodeContext) => string;
   decodeBytes: (
     text: string,
     context?: {
@@ -34,15 +26,7 @@ Provides a way to encode strings and bytes from and into Base64URL.
       };
     }
   ) => string;
-  encodeBytes: (
-    bytes: number[],
-    context?: {
-      btoa: (byteString: string) => string;
-      TextEncoder: new () => {
-        encode: (input?: string) => Uint8Array;
-      };
-    }
-  ) => string;
+  encodeBytes: (bytes: number[], context?: EncodeContext) => string;
   fromByteString: (byteString: string) => number[];
   toByteString: (bytes: number[]) => string;
 }
diff --git a/encoding/base64url.js b/encoding/base64url.js
index c7e9165e..6c6d1a70 100644
--- a/encoding/base64url.js
+++ b/encoding/base64url.js
@@ -5,7 +5,7 @@ export const toByteString = bytes =>
   bytes.map(_ => String.fromCharCode(_)).join("");
 
 export const fromByteString = byteString =>
-  [...byteString].map(_ => _.codePointAt(0));
+  [...byteString].map(_ => _.codePointAt(0) || 0);
 
 const ENCODING = "utf-8";
 
diff --git a/encoding/base64url.json b/encoding/base64url.json
index 78711552..34c52133 100644
--- a/encoding/base64url.json
+++ b/encoding/base64url.json
@@ -1,7 +1,7 @@
 {
   "name": "base64url",
   "description": "Provides a way to encode strings and bytes from and into Base64URL.",
-  "signature": "{\n  decode: (\n    text: string,\n    context?: {\n      atob: (byteString: string) => string;\n      TextDecoder: new (encoding: string) => {\n        decode: (input?: Uint8Array) => string;\n      };\n    }\n  ) => string;\n  decodeBytes: (\n    text: string,\n    context?: {\n      atob: (byteString: string) => string;\n      TextDecoder: new (encoding: string) => {\n        decode: (input?: Uint8Array) => string;\n      };\n    }\n  ) => number[];\n  encode: (\n    text: string,\n    context?: {\n      btoa: (byteString: string) => string;\n      TextEncoder: new () => {\n        encode: (input?: string) => Uint8Array;\n      };\n    }\n  ) => string;\n  encodeBytes: (\n    bytes: number[],\n    context?: {\n      btoa: (byteString: string) => string;\n      TextEncoder: new () => {\n        encode: (input?: string) => Uint8Array;\n      };\n    }\n  ) => string;\n  fromByteString: (byteString: string) => number[];\n  toByteString: (bytes: number[]) => string;\n}",
+  "signature": "{\n  decode: (text: string, context?: DecodeContext) => string;\n  decodeBytes: (\n    text: string,\n    context?: {\n      atob: (byteString: string) => string;\n      TextDecoder: new (encoding: string) => {\n        decode: (input?: Uint8Array) => string;\n      };\n    }\n  ) => number[];\n  encode: (\n    text: string,\n    context?: {\n      btoa: (byteString: string) => string;\n      TextEncoder: new () => {\n        encode: (input?: string) => Uint8Array;\n      };\n    }\n  ) => string;\n  encodeBytes: (bytes: number[], context?: EncodeContext) => string;\n  fromByteString: (byteString: string) => number[];\n  toByteString: (bytes: number[]) => string;\n}",
   "examples": [
     {
       "language": "javascript",
diff --git a/encoding/base64url.md b/encoding/base64url.md
index 08026f4b..78bb2f76 100644
--- a/encoding/base64url.md
+++ b/encoding/base64url.md
@@ -7,15 +7,7 @@ Provides a way to encode strings and bytes from and into Base64URL.
 <!-- prettier-ignore-start -->
 ```typescript
 {
-  decode: (
-    text: string,
-    context?: {
-      atob: (byteString: string) => string;
-      TextDecoder: new (encoding: string) => {
-        decode: (input?: Uint8Array) => string;
-      };
-    }
-  ) => string;
+  decode: (text: string, context?: DecodeContext) => string;
   decodeBytes: (
     text: string,
     context?: {
@@ -34,15 +26,7 @@ Provides a way to encode strings and bytes from and into Base64URL.
       };
     }
   ) => string;
-  encodeBytes: (
-    bytes: number[],
-    context?: {
-      btoa: (byteString: string) => string;
-      TextEncoder: new () => {
-        encode: (input?: string) => Uint8Array;
-      };
-    }
-  ) => string;
+  encodeBytes: (bytes: number[], context?: EncodeContext) => string;
   fromByteString: (byteString: string) => number[];
   toByteString: (bytes: number[]) => string;
 }
diff --git a/encoding/base64url.ts b/encoding/base64url.ts
index 75b5c93d..98c75bc4 100644
--- a/encoding/base64url.ts
+++ b/encoding/base64url.ts
@@ -1,23 +1,34 @@
 /* eslint-env browser, node */
 
+export interface EncodeContext {
+  btoa: (byteString: string) => string;
+  TextEncoder: new () => {
+    encode: { (input?: string): Uint8Array };
+  };
+}
+
+export interface DecodeContext {
+  atob: (byteString: string) => string;
+  TextDecoder: new (encoding: string) => {
+    decode: (input?: Uint8Array) => string;
+  };
+}
+
 const toArray = (typedArray: Uint8Array): number[] => [...typedArray];
 
 export const toByteString = (bytes: number[]) =>
   bytes.map(_ => String.fromCharCode(_)).join("");
 
-export const fromByteString = (byteString: string) =>
-  [...byteString].map(_ => _.codePointAt(0));
+export const fromByteString = (byteString: string): number[] =>
+  [...byteString].map(_ => _.codePointAt(0) || 0);
 
 const ENCODING = "utf-8";
 
 const btoaImplementation = (
   text: string,
-  context: {
-    btoa: (byteString: string) => string;
-    TextEncoder: new () => {
-      encode: { (input?: string): Uint8Array };
-    };
-  } = typeof window !== "undefined" ? window : undefined
+  context: EncodeContext | undefined = typeof window !== "undefined"
+    ? window
+    : undefined
 ) =>
   context
     ? context.btoa(
@@ -27,12 +38,9 @@ const btoaImplementation = (
 
 const atobImplementation = (
   text: string,
-  context: {
-    atob: (byteString: string) => string;
-    TextDecoder: new (encoding: string) => {
-      decode: (input?: Uint8Array) => string;
-    };
-  } = typeof window !== "undefined" ? window : undefined
+  context: DecodeContext | undefined = typeof window !== "undefined"
+    ? window
+    : undefined
 ) =>
   context
     ? new context.TextDecoder(ENCODING).decode(
@@ -52,15 +60,8 @@ export const encode = (
     .replace(/\+/g, "-")
     .replace(/\//g, "_");
 
-export const decode = (
-  text: string,
-  context?: {
-    atob: (byteString: string) => string;
-    TextDecoder: new (encoding: string) => {
-      decode: (input?: Uint8Array) => string;
-    };
-  }
-) => atobImplementation(text.replace(/-/g, "+").replace(/_/g, "/"), context);
+export const decode = (text: string, context?: DecodeContext) =>
+  atobImplementation(text.replace(/-/g, "+").replace(/_/g, "/"), context);
 
 export const toBase64Url = (base64: string) =>
   base64.replace(/\+/g, "-").replace(/\//g, "_");
@@ -68,13 +69,7 @@ export const toBase64Url = (base64: string) =>
 export const fromBase64Url = (base64: string) =>
   base64.replace(/-/g, "+").replace(/_/g, "/");
 
-export const encodeBytes = (
-  bytes: number[],
-  context?: {
-    btoa: (byteString: string) => string;
-    TextEncoder: new () => { encode: (input?: string) => Uint8Array };
-  }
-) => {
+export const encodeBytes = (bytes: number[], context?: EncodeContext) => {
   const sourceText = toByteString(bytes);
 
   return encode(sourceText, context);
diff --git a/function/memoizeWith.ts b/function/memoizeWith.ts
index 099dcf22..12f09e9a 100644
--- a/function/memoizeWith.ts
+++ b/function/memoizeWith.ts
@@ -1,10 +1,10 @@
 export default (equals: (x: any, y: any) => boolean) => (
   f: (...xs: any[]) => any
 ) => {
-  let memoized = undefined;
-  let memoizedArgs = undefined;
+  let memoized: any = undefined;
+  let memoizedArgs: any[] | undefined = undefined;
 
-  return (...args) => {
+  return (...args: any[]) => {
     if (memoized && equals(args, memoizedArgs)) {
       return memoized;
     }
diff --git a/is/README.md b/is/README.md
index d0d174b9..7b2cf479 100644
--- a/is/README.md
+++ b/is/README.md
@@ -94,6 +94,18 @@ Checks if given value is an integer.
 ```
 <!-- prettier-ignore-end -->
 
+# nonNullable
+
+Checks and asserts the given value is not a null or undefined.
+
+## Type signature
+
+<!-- prettier-ignore-start -->
+```typescript
+<T>(val: T) => val is NonNullable<T>
+```
+<!-- prettier-ignore-end -->
+
 # normal
 
 Checks if the given value is a number in a normal range [0, 1].
diff --git a/is/byte.js b/is/byte.js
index b25231df..2d422193 100644
--- a/is/byte.js
+++ b/is/byte.js
@@ -1,3 +1,4 @@
 import integer from "./integer.js";
+import nonNullable from "./nonNullable.js";
 
-export default x => integer(x) && x >= 0 && x <= 255;
+export default x => nonNullable(x) && integer(x) && x >= 0 && x <= 255;
diff --git a/is/byte.ts b/is/byte.ts
index 6afe9f0d..7eded0d0 100644
--- a/is/byte.ts
+++ b/is/byte.ts
@@ -1,3 +1,5 @@
 import integer from "./integer";
+import nonNullable from "./nonNullable";
 
-export default (x?: number) => integer(x) && x >= 0 && x <= 255;
+export default (x?: number) =>
+  nonNullable(x) && integer(x) && x >= 0 && x <= 255;
diff --git a/is/index.js b/is/index.js
index 2880557e..84d2ff61 100644
--- a/is/index.js
+++ b/is/index.js
@@ -4,6 +4,7 @@ import date from "./date.js";
 import defined from "./defined.js";
 import _function from "./function.js";
 import integer from "./integer.js";
+import nonNullable from "./nonNullable.js";
 import normal from "./normal.js";
 import number from "./number.js";
 import object from "./object.js";
@@ -16,6 +17,7 @@ export {
   defined,
   _function,
   integer,
+  nonNullable,
   normal,
   number,
   object,
@@ -29,6 +31,7 @@ export default {
   defined,
   _function,
   integer,
+  nonNullable,
   normal,
   number,
   object,
diff --git a/is/index.ts b/is/index.ts
index 0a1a25d4..524c029d 100644
--- a/is/index.ts
+++ b/is/index.ts
@@ -4,6 +4,7 @@ import date from "./date";
 import defined from "./defined";
 import _function from "./function";
 import integer from "./integer";
+import nonNullable from "./nonNullable";
 import normal from "./normal";
 import number from "./number";
 import object from "./object";
@@ -16,6 +17,7 @@ export {
   defined,
   _function,
   integer,
+  nonNullable,
   normal,
   number,
   object,
@@ -29,6 +31,7 @@ export default {
   defined,
   _function,
   integer,
+  nonNullable,
   normal,
   number,
   object,
diff --git a/is/integer.js b/is/integer.js
index b79db0fd..21e7e213 100644
--- a/is/integer.js
+++ b/is/integer.js
@@ -1,3 +1,4 @@
 import number from "./number.js";
+import nonNullable from "./nonNullable.js";
 
-export default x => number(x) && Math.floor(x) === x;
+export default x => nonNullable(x) && number(x) && Math.floor(x) === x;
diff --git a/is/integer.ts b/is/integer.ts
index 1cba338e..47aa7d65 100644
--- a/is/integer.ts
+++ b/is/integer.ts
@@ -1,3 +1,5 @@
 import number from "./number";
+import nonNullable from "./nonNullable";
 
-export default (x?: number) => number(x) && Math.floor(x) === x;
+export default (x?: number) =>
+  nonNullable(x) && number(x) && Math.floor(x) === x;
diff --git a/is/nonNullable.js b/is/nonNullable.js
new file mode 100644
index 00000000..6de4af85
--- /dev/null
+++ b/is/nonNullable.js
@@ -0,0 +1 @@
+export default val => val !== undefined && val !== null;
diff --git a/is/nonNullable.json b/is/nonNullable.json
new file mode 100644
index 00000000..a4eb5f36
--- /dev/null
+++ b/is/nonNullable.json
@@ -0,0 +1,12 @@
+{
+  "name": "nonNullable",
+  "description": "Checks and asserts the given value is not a null or undefined.",
+  "signature": "<T>(val: T) => val is NonNullable<T>",
+  "examples": [
+    {
+      "language": "javascript",
+      "content": "nonNullable(); // ⇒ TODO"
+    }
+  ],
+  "questions": ["TODO: List questions that may this function answers."]
+}
diff --git a/is/nonNullable.md b/is/nonNullable.md
new file mode 100644
index 00000000..c45d8e8f
--- /dev/null
+++ b/is/nonNullable.md
@@ -0,0 +1,11 @@
+# nonNullable
+
+Checks and asserts the given value is not a null or undefined.
+
+## Type signature
+
+<!-- prettier-ignore-start -->
+```typescript
+<T>(val: T) => val is NonNullable<T>
+```
+<!-- prettier-ignore-end -->
diff --git a/is/nonNullable.test.ts b/is/nonNullable.test.ts
new file mode 100644
index 00000000..7e75f049
--- /dev/null
+++ b/is/nonNullable.test.ts
@@ -0,0 +1,25 @@
+/* eslint-env jest */
+// @ts-ignore ambiguous import
+import nonNullable from "./nonNullable.ts";
+
+describe("nonNullable", () => {
+  it("checks and asserts the given value is not a null or undefined", () => {
+    expect(nonNullable(undefined)).toBe(false);
+    expect(nonNullable(null)).toBe(false);
+
+    expect(nonNullable(false)).toBe(true);
+    expect(nonNullable(0)).toBe(true);
+    expect(nonNullable("")).toBe(true);
+
+    expect(nonNullable({})).toBe(true);
+    expect(nonNullable([])).toBe(true);
+    expect(nonNullable(NaN)).toBe(true);
+    expect(nonNullable(() => {})).toBe(true);
+
+    expect(nonNullable("test")).toBe(true);
+    expect(nonNullable([1, 2, 3])).toBe(true);
+    expect(nonNullable({ a: 1, b: 2, c: 3 })).toBe(true);
+    expect(nonNullable(17.6)).toBe(true);
+    expect(nonNullable(Math.min)).toBe(true);
+  });
+});
diff --git a/is/nonNullable.ts b/is/nonNullable.ts
new file mode 100644
index 00000000..7979cfd9
--- /dev/null
+++ b/is/nonNullable.ts
@@ -0,0 +1,2 @@
+export default <T>(val: T): val is NonNullable<T> =>
+  val !== undefined && val !== null;
diff --git a/is/normal.js b/is/normal.js
index 284b2b93..16332193 100644
--- a/is/normal.js
+++ b/is/normal.js
@@ -1,3 +1,4 @@
 import number from "./number.js";
+import nonNullable from "./nonNullable.js";
 
-export default x => number(x) && x >= 0 && x <= 1;
+export default x => nonNullable(x) && number(x) && x >= 0 && x <= 1;
diff --git a/is/normal.ts b/is/normal.ts
index 2dc02f68..c75bd259 100644
--- a/is/normal.ts
+++ b/is/normal.ts
@@ -1,3 +1,4 @@
 import number from "./number";
+import nonNullable from "./nonNullable";
 
-export default (x?: number) => number(x) && x >= 0 && x <= 1;
+export default (x?: number) => nonNullable(x) && number(x) && x >= 0 && x <= 1;
diff --git a/is/number.js b/is/number.js
index 819511f5..492cfe77 100644
--- a/is/number.js
+++ b/is/number.js
@@ -1,2 +1,7 @@
+import nonNullable from "./nonNullable.js";
+
 export default x =>
-  typeof x === "number" && !Number.isNaN(x) && Number.isFinite(x);
+  nonNullable(x) &&
+  typeof x === "number" &&
+  !Number.isNaN(x) &&
+  Number.isFinite(x);
diff --git a/is/number.ts b/is/number.ts
index 102e7de3..f67dc8e9 100644
--- a/is/number.ts
+++ b/is/number.ts
@@ -1,2 +1,7 @@
+import nonNullable from "./nonNullable";
+
 export default (x?: any) =>
-  typeof x === "number" && !Number.isNaN(x) && Number.isFinite(x);
+  nonNullable(x) &&
+  typeof x === "number" &&
+  !Number.isNaN(x) &&
+  Number.isFinite(x);
diff --git a/math/median.ts b/math/median.ts
index a34e2de1..b332b629 100644
--- a/math/median.ts
+++ b/math/median.ts
@@ -1,7 +1,7 @@
 import sort from "../array/sort";
 import subtract from "./subtract";
 
-export default (xs?: number[]): number => {
+export default (xs?: number[]): number | undefined => {
   if (!xs || xs.length === 0) {
     return undefined;
   }
diff --git a/object/README.md b/object/README.md
index e4f57227..3a155675 100644
--- a/object/README.md
+++ b/object/README.md
@@ -297,7 +297,12 @@ Merges two objects deeply.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(a: object, b: object) => object
+(
+  a: {
+    [index: string]: any;
+  },
+  b: object
+) => object
 ```
 <!-- prettier-ignore-end -->
 
@@ -341,6 +346,8 @@ Sorts the given object by a comparator.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(f: any) => (xs: any) => object
+(
+  f: (a: any, b: any) => number
+) => (xs: object) => object
 ```
 <!-- prettier-ignore-end -->
diff --git a/object/merge.js b/object/merge.js
index 24fc832b..3a428175 100644
--- a/object/merge.js
+++ b/object/merge.js
@@ -1,12 +1,13 @@
+import isNonNullable from "../is/nonNullable.js";
 import isObject from "../is/object.js";
 import map from "./map.js";
 
-const isNonNullishObject = x => x !== undefined && x !== null && isObject(x);
+const isNonNullableObject = x => isNonNullable(x) && isObject(x);
 
 const merge = (a, b) => ({
   ...a,
   ...map((value, key) =>
-    isNonNullishObject(value) && isNonNullishObject(a[key])
+    isNonNullableObject(value) && isNonNullableObject(a[key])
       ? merge(a[key], value)
       : value
   )(b)
diff --git a/object/merge.json b/object/merge.json
index 8538d2ac..abd1806f 100644
--- a/object/merge.json
+++ b/object/merge.json
@@ -1,7 +1,7 @@
 {
   "name": "merge",
   "description": "Merges two objects deeply.",
-  "signature": "(a: object, b: object) => object",
+  "signature": "(\n  a: {\n    [index: string]: any;\n  },\n  b: object\n) => object",
   "examples": [
     {
       "language": "javascript",
diff --git a/object/merge.md b/object/merge.md
index d74ed2cd..6966e81a 100644
--- a/object/merge.md
+++ b/object/merge.md
@@ -6,7 +6,12 @@ Merges two objects deeply.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(a: object, b: object) => object
+(
+  a: {
+    [index: string]: any;
+  },
+  b: object
+) => object
 ```
 <!-- prettier-ignore-end -->
 
diff --git a/object/merge.ts b/object/merge.ts
index 7664e921..157c8c3a 100644
--- a/object/merge.ts
+++ b/object/merge.ts
@@ -1,13 +1,13 @@
+import isNonNullable from "../is/nonNullable";
 import isObject from "../is/object";
 import map from "./map";
 
-const isNonNullishObject = (x?: object) =>
-  x !== undefined && x !== null && isObject(x);
+const isNonNullableObject = (x?: object) => isNonNullable(x) && isObject(x);
 
-const merge = (a: object, b: object): object => ({
+const merge = (a: { [index: string]: any }, b: object): object => ({
   ...a,
   ...map((value, key) =>
-    isNonNullishObject(value) && isNonNullishObject(a[key])
+    isNonNullableObject(value) && isNonNullableObject(a[key])
       ? merge(a[key], value)
       : value
   )(b)
diff --git a/object/sort.json b/object/sort.json
index 423a3e4a..2f1bbb63 100644
--- a/object/sort.json
+++ b/object/sort.json
@@ -1,7 +1,7 @@
 {
   "name": "sort",
   "description": "Sorts the given object by a comparator.",
-  "signature": "(f: any) => (xs: any) => object",
+  "signature": "(\n  f: (a: any, b: any) => number\n) => (xs: object) => object",
   "examples": [
     {
       "language": "javascript",
diff --git a/object/sort.md b/object/sort.md
index d6515960..0e678206 100644
--- a/object/sort.md
+++ b/object/sort.md
@@ -6,6 +6,8 @@ Sorts the given object by a comparator.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(f: any) => (xs: any) => object
+(
+  f: (a: any, b: any) => number
+) => (xs: object) => object
 ```
 <!-- prettier-ignore-end -->
diff --git a/object/sort.ts b/object/sort.ts
index ce7b9167..31e9848e 100644
--- a/object/sort.ts
+++ b/object/sort.ts
@@ -2,5 +2,5 @@ import sort from "../array/sort";
 import entries from "./entries";
 import fromEntries from "./fromEntries";
 
-export default f => xs =>
+export default (f: (a: any, b: any) => number) => (xs: object): object =>
   fromEntries(sort(([, a], [, b]) => f(a, b))(entries(xs)));
diff --git a/query/README.md b/query/README.md
index 5dbadca9..2ab9105d 100644
--- a/query/README.md
+++ b/query/README.md
@@ -30,6 +30,6 @@ Serializes the given object into a query string.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(xs?: {}) => string
+(xs?: { [index: string]: any }) => string
 ```
 <!-- prettier-ignore-end -->
diff --git a/query/serialize.js b/query/serialize.js
index 130a257e..681ea6b9 100644
--- a/query/serialize.js
+++ b/query/serialize.js
@@ -3,7 +3,7 @@ import entries from "../object/entries.js";
 export default (xs = {}) =>
   entries(xs)
     .filter(([, value]) => Boolean(value) || value === 0)
-    .map(pair => pair.map(encodeURIComponent))
+    .map(pair => pair.map(value => encodeURIComponent(value)))
     .reduce(
       (acc, [key, value]) => [
         ...acc,
diff --git a/query/serialize.json b/query/serialize.json
index 041609ef..3d7f3e50 100644
--- a/query/serialize.json
+++ b/query/serialize.json
@@ -1,7 +1,7 @@
 {
   "name": "serialize",
   "description": "Serializes the given object into a query string.",
-  "signature": "(xs?: {}) => string",
+  "signature": "(xs?: { [index: string]: any }) => string",
   "examples": [
     {
       "language": "javascript",
diff --git a/query/serialize.md b/query/serialize.md
index 489d0be2..64666971 100644
--- a/query/serialize.md
+++ b/query/serialize.md
@@ -6,6 +6,6 @@ Serializes the given object into a query string.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(xs?: {}) => string
+(xs?: { [index: string]: any }) => string
 ```
 <!-- prettier-ignore-end -->
diff --git a/query/serialize.ts b/query/serialize.ts
index 91ce6262..bd01c100 100644
--- a/query/serialize.ts
+++ b/query/serialize.ts
@@ -1,9 +1,9 @@
 import entries from "../object/entries";
 
-export default (xs = {}) =>
+export default (xs: { [index: string]: any } = {}): string =>
   entries(xs)
     .filter(([, value]) => Boolean(value) || value === 0)
-    .map(pair => pair.map(encodeURIComponent))
+    .map(pair => pair.map(value => encodeURIComponent(value)))
     .reduce(
       (acc, [key, value]) => [
         ...acc,
diff --git a/range/README.md b/range/README.md
index 8f3eab5e..34683952 100644
--- a/range/README.md
+++ b/range/README.md
@@ -6,7 +6,7 @@ Checks if the given range is empty.
 
 <!-- prettier-ignore-start -->
 ```typescript
-([min, max]: [any, any]) => boolean
+([min, max]: [number, number]) => boolean
 ```
 <!-- prettier-ignore-end -->
 
@@ -27,7 +27,10 @@ Checks if the given ranges are equal.
 
 <!-- prettier-ignore-start -->
 ```typescript
-([a, b]: [any, any], [c, d]: [any, any]) => boolean
+(
+  [a, b]: [number, number],
+  [c, d]: [number, number]
+) => boolean
 ```
 <!-- prettier-ignore-end -->
 
@@ -39,7 +42,7 @@ Computes the signed length of the given range.
 
 <!-- prettier-ignore-start -->
 ```typescript
-([min, max]: [any, any]) => number
+([min, max]: [number, number]) => number
 ```
 <!-- prettier-ignore-end -->
 
diff --git a/range/empty.json b/range/empty.json
index 63c09b2a..b6a44e18 100644
--- a/range/empty.json
+++ b/range/empty.json
@@ -1,7 +1,7 @@
 {
   "name": "empty",
   "description": "Checks if the given range is empty.",
-  "signature": "([min, max]: [any, any]) => boolean",
+  "signature": "([min, max]: [number, number]) => boolean",
   "examples": [
     {
       "language": "javascript",
diff --git a/range/empty.md b/range/empty.md
index 16fda656..902a2436 100644
--- a/range/empty.md
+++ b/range/empty.md
@@ -6,7 +6,7 @@ Checks if the given range is empty.
 
 <!-- prettier-ignore-start -->
 ```typescript
-([min, max]: [any, any]) => boolean
+([min, max]: [number, number]) => boolean
 ```
 <!-- prettier-ignore-end -->
 
diff --git a/range/empty.ts b/range/empty.ts
index 71065567..d607d8aa 100644
--- a/range/empty.ts
+++ b/range/empty.ts
@@ -1 +1 @@
-export default ([min, max]) => min === max;
+export default ([min, max]: [number, number]): boolean => min === max;
diff --git a/range/equals.json b/range/equals.json
index 6e0992e8..c4023ff4 100644
--- a/range/equals.json
+++ b/range/equals.json
@@ -1,7 +1,7 @@
 {
   "name": "equals",
   "description": "Checks if the given ranges are equal.",
-  "signature": "([a, b]: [any, any], [c, d]: [any, any]) => boolean",
+  "signature": "(\n  [a, b]: [number, number],\n  [c, d]: [number, number]\n) => boolean",
   "examples": [
     {
       "language": "javascript",
diff --git a/range/equals.md b/range/equals.md
index 0210ff5a..2fd47b77 100644
--- a/range/equals.md
+++ b/range/equals.md
@@ -6,6 +6,9 @@ Checks if the given ranges are equal.
 
 <!-- prettier-ignore-start -->
 ```typescript
-([a, b]: [any, any], [c, d]: [any, any]) => boolean
+(
+  [a, b]: [number, number],
+  [c, d]: [number, number]
+) => boolean
 ```
 <!-- prettier-ignore-end -->
diff --git a/range/equals.ts b/range/equals.ts
index ab5c1860..2527842e 100644
--- a/range/equals.ts
+++ b/range/equals.ts
@@ -1 +1,2 @@
-export default ([a, b], [c, d]) => a === c && b === d;
+export default ([a, b]: [number, number], [c, d]: [number, number]): boolean =>
+  a === c && b === d;
diff --git a/range/length.json b/range/length.json
index 5436cc92..af5a5465 100644
--- a/range/length.json
+++ b/range/length.json
@@ -1,7 +1,7 @@
 {
   "name": "length",
   "description": "Computes the signed length of the given range.",
-  "signature": "([min, max]: [any, any]) => number",
+  "signature": "([min, max]: [number, number]) => number",
   "examples": [
     {
       "language": "javascript",
diff --git a/range/length.md b/range/length.md
index dc0e39a3..a8b8dc28 100644
--- a/range/length.md
+++ b/range/length.md
@@ -6,6 +6,6 @@ Computes the signed length of the given range.
 
 <!-- prettier-ignore-start -->
 ```typescript
-([min, max]: [any, any]) => number
+([min, max]: [number, number]) => number
 ```
 <!-- prettier-ignore-end -->
diff --git a/range/length.ts b/range/length.ts
index 3961ffcd..1963a21b 100644
--- a/range/length.ts
+++ b/range/length.ts
@@ -1 +1 @@
-export default ([min, max]) => max - min;
+export default ([min, max]: [number, number]): number => max - min;
diff --git a/tsconfig.json b/tsconfig.json
index bc4c76cd..85e96f61 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -2,9 +2,10 @@
   "compilerOptions": {
     "module": "ES6",
     "noImplicitAny": true,
-    "removeComments": true,
     "preserveConstEnums": true,
+    "removeComments": true,
     "sourceMap": true,
+    "strict": true,
     "target": "ES2020"
   }
 }
diff --git a/vector2/README.md b/vector2/README.md
index 0f2cf614..7dc3a640 100644
--- a/vector2/README.md
+++ b/vector2/README.md
@@ -40,7 +40,10 @@ Calculates a cross product of the given vectors. Returns a scalar.
 
 <!-- prettier-ignore-start -->
 ```typescript
-([a, b]: [any, any], [c, d]: [any, any]) => number
+(
+  [a, b]: [number, number],
+  [c, d]: [number, number]
+) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -52,7 +55,10 @@ Calculates a dot product of the given vectors. Returns a scalar.
 
 <!-- prettier-ignore-start -->
 ```typescript
-([a, b]: [any, any], [c, d]: [any, any]) => number
+(
+  [a, b]: [number, number],
+  [c, d]: [number, number]
+) => number
 ```
 <!-- prettier-ignore-end -->
 
@@ -141,7 +147,7 @@ Normalizes the given vector. Returns [0, 0] vector for points.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(vector: [number, number]) => number[]
+(vector: [number, number]) => [number, number]
 ```
 <!-- prettier-ignore-end -->
 
diff --git a/vector2/cross.json b/vector2/cross.json
index ce55aa65..9214f26a 100644
--- a/vector2/cross.json
+++ b/vector2/cross.json
@@ -1,7 +1,7 @@
 {
   "name": "cross",
   "description": "Calculates a cross product of the given vectors. Returns a scalar.",
-  "signature": "([a, b]: [any, any], [c, d]: [any, any]) => number",
+  "signature": "(\n  [a, b]: [number, number],\n  [c, d]: [number, number]\n) => number",
   "examples": [
     {
       "language": "javascript",
diff --git a/vector2/cross.md b/vector2/cross.md
index ee43d9e1..72f7b55b 100644
--- a/vector2/cross.md
+++ b/vector2/cross.md
@@ -6,6 +6,9 @@ Calculates a cross product of the given vectors. Returns a scalar.
 
 <!-- prettier-ignore-start -->
 ```typescript
-([a, b]: [any, any], [c, d]: [any, any]) => number
+(
+  [a, b]: [number, number],
+  [c, d]: [number, number]
+) => number
 ```
 <!-- prettier-ignore-end -->
diff --git a/vector2/cross.ts b/vector2/cross.ts
index 327ae4d7..6b3fe15c 100644
--- a/vector2/cross.ts
+++ b/vector2/cross.ts
@@ -1 +1,2 @@
-export default ([a, b], [c, d]) => a * d - b * c;
+export default ([a, b]: [number, number], [c, d]: [number, number]): number =>
+  a * d - b * c;
diff --git a/vector2/dot.json b/vector2/dot.json
index a61d5e30..1052dc37 100644
--- a/vector2/dot.json
+++ b/vector2/dot.json
@@ -1,7 +1,7 @@
 {
   "name": "dot",
   "description": "Calculates a dot product of the given vectors. Returns a scalar.",
-  "signature": "([a, b]: [any, any], [c, d]: [any, any]) => number",
+  "signature": "(\n  [a, b]: [number, number],\n  [c, d]: [number, number]\n) => number",
   "examples": [
     {
       "language": "javascript",
diff --git a/vector2/dot.md b/vector2/dot.md
index f307618b..bee5beb8 100644
--- a/vector2/dot.md
+++ b/vector2/dot.md
@@ -6,6 +6,9 @@ Calculates a dot product of the given vectors. Returns a scalar.
 
 <!-- prettier-ignore-start -->
 ```typescript
-([a, b]: [any, any], [c, d]: [any, any]) => number
+(
+  [a, b]: [number, number],
+  [c, d]: [number, number]
+) => number
 ```
 <!-- prettier-ignore-end -->
diff --git a/vector2/dot.ts b/vector2/dot.ts
index c18e85fe..bc211e9e 100644
--- a/vector2/dot.ts
+++ b/vector2/dot.ts
@@ -1 +1,2 @@
-export default ([a, b], [c, d]) => a * c + b * d;
+export default ([a, b]: [number, number], [c, d]: [number, number]): number =>
+  a * c + b * d;
diff --git a/vector2/normalize.js b/vector2/normalize.js
index 49c0c810..c843a3d6 100644
--- a/vector2/normalize.js
+++ b/vector2/normalize.js
@@ -2,6 +2,7 @@ import length from "./length.js";
 
 export default vector => {
   const magnitude = length(vector);
+  const [x, y] = vector;
 
-  return magnitude !== 0 ? vector.map(_ => _ / magnitude) : vector;
+  return magnitude !== 0 ? [x / magnitude, y / magnitude] : vector;
 };
diff --git a/vector2/normalize.json b/vector2/normalize.json
index a81ef5de..026e6a0e 100644
--- a/vector2/normalize.json
+++ b/vector2/normalize.json
@@ -1,7 +1,7 @@
 {
   "name": "normalize",
   "description": "Normalizes the given vector. Returns [0, 0] vector for points.",
-  "signature": "(vector: [number, number]) => number[]",
+  "signature": "(vector: [number, number]) => [number, number]",
   "examples": [
     {
       "language": "javascript",
diff --git a/vector2/normalize.md b/vector2/normalize.md
index 17717177..04849d18 100644
--- a/vector2/normalize.md
+++ b/vector2/normalize.md
@@ -6,6 +6,6 @@ Normalizes the given vector. Returns [0, 0] vector for points.
 
 <!-- prettier-ignore-start -->
 ```typescript
-(vector: [number, number]) => number[]
+(vector: [number, number]) => [number, number]
 ```
 <!-- prettier-ignore-end -->
diff --git a/vector2/normalize.ts b/vector2/normalize.ts
index 0a6954ab..d9c9da03 100644
--- a/vector2/normalize.ts
+++ b/vector2/normalize.ts
@@ -1,7 +1,9 @@
 import length from "./length";
 
-export default (vector: [number, number]) => {
+export default (vector: [number, number]): [number, number] => {
   const magnitude = length(vector);
 
-  return magnitude !== 0 ? vector.map(_ => _ / magnitude) : vector;
+  const [x, y] = vector;
+
+  return magnitude !== 0 ? [x / magnitude, y / magnitude] : vector;
 };
diff --git a/web/README.md b/web/README.md
index a8c5128e..a20ace5e 100644
--- a/web/README.md
+++ b/web/README.md
@@ -41,10 +41,10 @@ Tests if the current event seems like an intent to open a new tab. Useful for cl
   metaKey,
   shiftKey
 }: {
-  button: any;
-  ctrlKey: any;
-  metaKey: any;
-  shiftKey: any;
+  button?: number;
+  ctrlKey?: boolean;
+  metaKey?: boolean;
+  shiftKey?: boolean;
 }) => boolean
 ```
 <!-- prettier-ignore-end -->
diff --git a/web/events/README.md b/web/events/README.md
index cc6dbfb7..f487b478 100644
--- a/web/events/README.md
+++ b/web/events/README.md
@@ -27,10 +27,10 @@ Tests if the current event seems like an intent to open a new tab. Useful for cl
   metaKey,
   shiftKey
 }: {
-  button: any;
-  ctrlKey: any;
-  metaKey: any;
-  shiftKey: any;
+  button?: number;
+  ctrlKey?: boolean;
+  metaKey?: boolean;
+  shiftKey?: boolean;
 }) => boolean
 ```
 <!-- prettier-ignore-end -->
diff --git a/web/events/openInNewTabIntent.json b/web/events/openInNewTabIntent.json
index aef9d1bb..4e5b4791 100644
--- a/web/events/openInNewTabIntent.json
+++ b/web/events/openInNewTabIntent.json
@@ -1,7 +1,7 @@
 {
   "name": "openInNewTabIntent",
   "description": "Tests if the current event seems like an intent to open a new tab. Useful for client-side navigation handling.",
-  "signature": "({\n  button,\n  ctrlKey,\n  metaKey,\n  shiftKey\n}: {\n  button: any;\n  ctrlKey: any;\n  metaKey: any;\n  shiftKey: any;\n}) => boolean",
+  "signature": "({\n  button,\n  ctrlKey,\n  metaKey,\n  shiftKey\n}: {\n  button?: number;\n  ctrlKey?: boolean;\n  metaKey?: boolean;\n  shiftKey?: boolean;\n}) => boolean",
   "examples": [
     {
       "language": "javascript",
diff --git a/web/events/openInNewTabIntent.md b/web/events/openInNewTabIntent.md
index 93b3f02a..2e522bc7 100644
--- a/web/events/openInNewTabIntent.md
+++ b/web/events/openInNewTabIntent.md
@@ -12,10 +12,10 @@ Tests if the current event seems like an intent to open a new tab. Useful for cl
   metaKey,
   shiftKey
 }: {
-  button: any;
-  ctrlKey: any;
-  metaKey: any;
-  shiftKey: any;
+  button?: number;
+  ctrlKey?: boolean;
+  metaKey?: boolean;
+  shiftKey?: boolean;
 }) => boolean
 ```
 <!-- prettier-ignore-end -->
diff --git a/web/events/openInNewTabIntent.ts b/web/events/openInNewTabIntent.ts
index a44945b7..5dba11d4 100644
--- a/web/events/openInNewTabIntent.ts
+++ b/web/events/openInNewTabIntent.ts
@@ -1,2 +1,11 @@
-export default ({ button, ctrlKey, metaKey, shiftKey }) =>
-  Boolean(ctrlKey || shiftKey || metaKey || button === 1);
+export default ({
+  button,
+  ctrlKey,
+  metaKey,
+  shiftKey
+}: {
+  button?: number;
+  ctrlKey?: boolean;
+  metaKey?: boolean;
+  shiftKey?: boolean;
+}) => Boolean(ctrlKey || shiftKey || metaKey || button === 1);