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Add typed return for Object.defineProperties #41424

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Add typed return for Object.defineProperties#41424
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Awaiting More FeedbackThis means we'd like to hear from more people who would be helped by this featureSuggestionAn idea for TypeScript

Description

@clshortfuse
Carlos Lopez (clshortfuse)
opened on Nov 6, 2020

Search Terms

Object.defineProperties typed

Suggestion

const newObject = Object.defineProperties(o, map);

Use Cases

Creating extensions of certain properties while still being able to type-check them

Examples

/** @type {NodeList} */
const nodeListObject = Object.defineProperties(/** @type {Node[]} */ ([]), {
    item: {
      enumerable: false,
      /** @param {number} [index] */
      value: function item(index) { return this[index]; },
    },
  });

Checklist

My suggestion meets these guidelines:

  • This wouldn't be a breaking change in existing TypeScript/JavaScript code
  • 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.

The current type I'm using is the following:

interface ObjectConstructor {
  defineProperties<T1, T2 = PropertyDescriptorMap>(o: T1, properties: T2 & ThisType<T1>): T1 & {
        [K in keyof T2]: (
          T2[K]['get'] extends Function ? ReturnType<T2[K]['get']> :
          T2[K]['set'] extends Function ? Parameters<T2[K]['set']>[0] :
          T2[K]['value'] extends undefined ? any : T2[K]['value']
        )
      };
}

It seems alright but I would love to get some feedback. Currently, I'm targeting against .get() first, then .set(arg0) and finally .value.

See: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperties

Activity

  1. ExE-Boss commented on Nov 6, 2020

    @ExE-Boss
    ExE Boss (ExE-Boss)
    on Nov 6, 2020
    Contributor

    Yours won’t correctly handle non‑writable properties, whereas mine is much more correct:

    interface ObjectConstructor {
	defineProperty<
		T,
		P extends PropertyKey,
		V = P extends keyof T ? T[P] : unknown,
		W = P extends keyof T ? true : false
	>(
		target: T,
		property: P,
		descriptor: TypedPropertyDescriptor<V> & { readonly writable?: W },
	): (T &
		{ readonly [K in P as W extends false ? K : never]: V } &
		{ -readonly [K in P as W extends true ? K : never]: V })
		// Needs https://github.com/microsoft/TypeScript/issues/40562:
		// & (asserts target is T &
		//	{ readonly [K in P as W extends false ? K : never]: V } &
		//	{ -readonly [K in P as W extends true ? K : never]: V });

	defineProperties<
		T,
		M extends Record<string | symbol, PropertyDescriptor>
	>(
		target: T,
		properties: M & ThisType<T>,
	): ({} extends M ? T : T & {
			readonly [K in keyof M as M[K] extends { readonly writable: false } ? K : (K extends keyof T ? never : K)]:
				M[K] extends Readonly<TypedPropertyDescriptor<infer V>> ? V : any;
		} & {
			-readonly [K in keyof M as M[K] extends { readonly writable: true } ? K : (K extends keyof T ? K : never)]:
				M[K] extends Readonly<TypedPropertyDescriptor<infer V>> ? V : any;
		})
		// Needs https://github.com/microsoft/TypeScript/issues/40562:
		// & (asserts target is ({} extends M ? T : T & {
		//	readonly [K in keyof M as M[K] extends { readonly writable: false } ? K : (K extends keyof T ? never : K)]:
		//		M[K] extends Readonly<TypedPropertyDescriptor<infer V>> ? V : any;
		// } & {
		//	-readonly [K in keyof M as M[K] extends { readonly writable: true } ? K : (K extends keyof T ? K : never)]:
		//		M[K] extends Readonly<TypedPropertyDescriptor<infer V>> ? V : any;
		// }))
}

  2. clshortfuse commented on Nov 6, 2020

    @clshortfuse
    Carlos Lopez (clshortfuse)
    on Nov 6, 2020
    Author

    Ah, I didn't see TypedPropertyDescriptor which would make things much easier. Any reason why this isn't part of the typings?

  3. ExE-Boss commented on Nov 7, 2020

    @ExE-Boss
    ExE Boss (ExE-Boss)
    on Nov 7, 2020
    Contributor

    Carlos Lopez (@clshortfuse)
    It’s probably for legacy compatibility.

    Which is probably the same reason as to why strictBindCallApply is not the default.

  4. Ryan Cavanaugh (RyanCavanaugh)
    added
    Awaiting More FeedbackThis means we'd like to hear from more people who would be helped by this feature
    SuggestionAn idea for TypeScript
    on Nov 11, 2020

  5. ExE-Boss commented on Mar 10, 2021

    @ExE-Boss
    ExE Boss (ExE-Boss)
    on Mar 10, 2021
    Contributor

    PR #42424 seems to be a start towards addressing this.

  6. edemaine commented on Jan 26, 2022

    @edemaine
    Erik Demaine (edemaine)
    on Jan 26, 2022

    ExE Boss (@ExE-Boss) Your definition seems far more useful. Perhaps it would make sense to turn into a PR? Is #40562 essential?

    Adding proper definitions of Object.defineProperties would be one way to approach getters/setters in CoffeeScript, which doesn't currently have built-in support so recommends using defineProperty. Lack of TypeScript support came up in this discussion.

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