Add typed return for Object.defineProperties

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

Start with the Object.defineProperties entry point and the proposed ObjectConstructor signature. Check how the example's get, set, and value cases should produce a typed result, using the compatibility and design-goal checklist as constraints; done means the requested return typing is supported without runtime changes.