microsoft / microsoft/TypeScript

Add typed overloads to `Object.create`

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Description

Search Terms

  • object.create
  • object create
  • typed object.create
  • typed object create

Suggestion

Change the signatures of Object.create to:

interface ObjectConstructor {
	create<P extends object | null>(proto: P): null extends P ? {} : P;

	create<
		P extends object | null,
		M extends PropertyDescriptorMap = {}
	>(proto: P, properties?: M & ThisType<any>): {
		readonly [
			K in keyof M as M[K] extends { readonly writable: false }
				? K
				: never
		]: M[K] extends Readonly<TypedPropertyDescriptor<infer V>>
			? V
			: any;
	} & {
		-readonly [
			K in keyof M as M[K] extends { readonly writable: true }
				? K
				: never
		]: M[K] extends Readonly<TypedPropertyDescriptor<infer V>>
			? V
			: any;
	} & (null extends P ? {} : P);
}

Use Cases

Getting correct types in code that does:

// `foo` is `any`, because `T` of Object.assign<T, U> is `any`:
const foo = Object.assign(
	// `T` is currently typed as `any`:
	Object.create(null),

	// Only `U` is typed correctly as { bar: number; baz: string }:
	{
		bar: 123,
		baz: 'biz',
	},
);

Examples

Checklist

My suggestion meets these guidelines:

  • This wouldn't be a breaking change in existing TypeScript/JavaScript code
    • This might need a flag similar to strictBindCallApply, or just done in a separate lib file.
  • This wouldn't change the runtime behavior of existing JavaScript code
  • This could be implemented without emitting different JS based on the types of the expressions
  • This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
  • This feature would agree with the rest of TypeScript's Design Goals.

Relevant issues

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the proposed ObjectConstructor.create overloads and the linked issues #1108, #13206, #18609, #38385, and #41424. Determine how the current library declarations and compatibility concerns should be handled; done means Object.create provides the requested type information without changing JavaScript runtime behavior.

Written by the indexing model from the issue text.

Assessment

Tech stack
typescript
Domain
compilers
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
38/100

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