lib.d.ts Function.bind with this

[bluelovers]

Search Terms

Suggestion

i don't know what is better name for ITSOverwriteThisFunction

interface Function2 extends Function
{
	bind<T extends any, F extends (...args: any[]) => any>(this: F, thisArg: T, ...argArray: any[]): ITSOverwriteThisFunction<T, F>;
}

export type ITSOverwriteThisFunction<T extends any, F extends (...args: any[]) => any> =
	(this: T, ...args: Parameters<F>) => ReturnType<F>

Use Cases

1. we can now let fn.bind, know who is this

problem: current typescript not support overload function, so this has limit

Examples

this examples looks so stupid, but i don't know how to make look better

export interface t4 extends Function2
{
	(): string
}

export declare let t5: t4

export let t6 = t5.bind([] as string[])

t6 = function ()
{
	this.includes('') // => this is string[]

	return ''
}

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.

[DanielRosenwasser]

I'm a little bit confused over what's being suggested here, but is it covered by #27028 which is coming in TypeScript 3.2?

[bluelovers]

@DanielRosenwasser

i think it not same,

in t6, ts know it is string[], so will show error when use this.padEnd(1, '0')

but in t9 , ts didn't show error

export interface t4 extends Function2
{
	(): string
}

export declare let t5: t4

export let t6 = t5.bind([] as string[])

t6 = function ()
{
	this.includes('') // => this is string[]

	// ts will and should show error
	this.padEnd(1, '0')
	
	return ''
}

export interface t7 extends Function
{
	(): string
}

export declare let t8: t7

export let t9 = t8.bind([] as string[])

t9 = function ()
{
	this.includes('') // => this is string[]

	// ts didn't show error
	this.padEnd(1, '0')

	return ''
}

[DanielRosenwasser]

I think that's because you extended Function, so all the "wrong" methods for bind are present. If you remove that, TS3.2 will resolve bind from a new type called CallableFunction. Can you verify whether that works?

[bluelovers]

my version is 3.2.0-dev.20181114

export interface t10
{
	(): string
}

export declare let t11: t10

export let t12 = t11.bind([] as string[])

t12 = function ()
{
	this.includes('') // => this is string[]

	// ts didn't show error
	this.padEnd(1, '0')

	return ''
}

export declare function t13()
export let t14 = t13.bind([] as string[])

t14 = function ()
{
	this.includes('') // => this is string[]

	// ts didn't show error
	this.padEnd(1, '0')

	return ''
}

[RyanCavanaugh]

I can't tell what's going on here. The posted code is full of errors and I don't see which ones are supposed to be good or bad. Please open a new issue with a clear description if needed. Thanks!