feat(micro-dash): improve the typing of omit()

projects/micro-dash/src/lib/interfaces.ts

@@ -3,7 +3,7 @@ export type Nil = null | undefined;
 /** @hidden */
 export type Primitive = boolean | number | string;
 /** @hidden */
-export type Key = keyof any;
+export type Key = keyof any; // TODO: replace with built-in PropertyKey
 /** @hidden */
 export type Existent = Primitive | object;
 /** @hidden */

projects/micro-dash/src/lib/object/omit.spec.ts

@@ -33,8 +33,8 @@ describe('omit()', () => {
   });
 
   it('should return an empty object when `object` is nullish', () => {
-    expect(omit<any>(null, 'valueOf')).toEqual({});
-    expect(omit<any>(undefined, 'valueOf')).toEqual({});
+    expect(omit<any, any>(null, 'valueOf')).toEqual({});
+    expect(omit<any, any>(undefined, 'valueOf')).toEqual({});
   });
 
   it('should not mutate `object`', () => {

projects/micro-dash/src/lib/object/omit.ts

@@ -1,6 +1,11 @@
 import { Nil } from '../interfaces';
 import { clone } from '../lang';
 
+/** @hidden */
+type RemainingKeys<T, Omits> =
+  | Exclude<keyof T, Omits>
+  | Extract<PropertyKey, keyof T>; // always include index properties
+
 /**
  * The opposite of `pick`; this method creates an object composed of the own enumerable string properties of object that are not omitted.
  *
@@ -12,10 +17,12 @@ import { clone } from '../lang';
  * - Lodash: 15,567 bytes
  * - Micro-dash: 155 bytes
  */
-export function omit<T extends object | Nil>(
+export function omit<T extends object | Nil, O extends Array<keyof T>>(
   object: T,
-  ...paths: Array<keyof T>
-): Partial<T> {
+  ...paths: O
+): {
+  [K in RemainingKeys<T, O[number]>]: T[K];
+} {
   const obj: any = clone(object) || {};
   for (const path of paths) {
     delete obj[path];

projects/micro-dash/src/typing-tests/object/omit.dts-spec.ts

@@ -0,0 +1,44 @@
+import { omit } from '../../lib/object';
+
+declare const str: string;
+declare const num: number;
+
+declare const obj: {
+  a: number;
+  b: Date;
+};
+// $ExpectType { a: number; }
+omit(obj, 'b');
+
+declare const indexed: {
+  [k: string]: number;
+  [k: number]: number;
+};
+// $ExpectType { [x: string]: number; [x: number]: number; }
+omit(indexed, 'hi');
+// $ExpectType { [x: string]: number; [x: number]: number; }
+omit(indexed, 5);
+// $ExpectType { [x: string]: number; [x: number]: number; }
+omit(indexed, 'hi', 5);
+// $ExpectType { [x: string]: number; [x: number]: number; }
+omit(indexed, str);
+
+declare const record: Record<string, number>;
+// $ExpectType { [x: string]: number; }
+omit(record, str);
+
+declare const composite: {
+  [k: number]: Date;
+  a: 'eh';
+  b: 'bee';
+};
+// $ExpectType { [x: number]: Date; b: "bee"; }
+omit(composite, 'a');
+// $ExpectType { [x: number]: Date; }
+omit(composite, 'a', 'b');
+// $ExpectType { [x: number]: Date; a: "eh"; b: "bee"; }
+omit(composite, 1);
+// $ExpectType { [x: number]: Date; a: "eh"; b: "bee"; }
+omit(composite, num);
+// $ExpectType { [x: number]: Date; b: "bee"; }
+omit(composite, num, 'a');