[Proposal] change Object.create in lib.d.ts

[texastoland]

Search Terms

object create null

Suggestion

Change Object.create in lib.d.ts.

namespace Object {
  export type NullPrototype = Record<keyof Object, never>
}

interface ObjectConstructor {
  create
    <T extends object | null>
    (proto: T):
    T extends null ? Object.NullPrototype : T
}

Use Cases

#1108

Examples

Playground

interface IDictLike<T> {[key: string]: T}
type DictLike = IDictLike<string> & Object.NullPrototype
const dictLike: DictLike = Object.create(null)

console.log(dictLike.key)
console.log(dictLike.toString())
//          ^^^^^^^^^^^^^^^^^^^
// Cannot invoke an expression whose type lacks a call signature.
// Type 'never' has no compatible call signatures.

// Same type as Object.create(Array.prototype)
const arrayLike = Object.create([])
console.log(arrayLike.key)
//                    ^^^
// Property 'key' does not exist on type 'any[]'. Did you mean 'keys'?
console.log(arrayLike.toString())

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. new expression-level syntax)

[RyanCavanaugh]

This is a breaking change. The problem here is that you end up creating a poisoned object where you can't use those fields at all -- this code becomes illegal:

const x = Object.create(null);
// Error, can't assign () => string to never
x.toString = () => "";

It also doesn't catch errors in places where you'd presumably want it to:

function fn(obj: { toString(): string }) { obj.toString() };
const x = Object.create(null);
// No error; crashes
fn(x);

[texastoland]

👍🏽 makes sense.