Enforce typings when using bind

Question

I'm trying to create a bound version of a function which has its arguments pre-set however I am unable to get any sort of type checks on the bind method.

Here's my code:

interface I {
  a: string;
  b: string;
}

function doSomethingWithValue(value: I) {
  // Do something
}

const ivalue: I = { a: 'a', b: 'b' };

// No error as expected.
doSomethingWithValue(ivalue);

//"Argument of type '"a"' is not assignable to parameter of type 'I'" as expected.
doSomethingWithValue('a');

// No error. Not what I expected
const bound = doSomethingWithValue.bind(null, 'a');

// Will fail
bound();

It seems that currently the TypeScript signature of bind is

bind(this: Function, thisArg: any, ...argArray: any[]): any;

Is there any way I could get types checks to work correctly with bind?

I've tried creating an index.d.ts but I am stuck on how to declare function parameters as a generic.

score 4 · Accepted Answer · answered Mar 20 '19 at 11:08

There is compiler option in 3.2 and newer, called strictBindCallApply documented here. You can also just enable strict which also enables strictBindCallApply

With this option active you will get an error on this line:

const bound = doSomethingWithValue.bind(null, 'a');

score -2 · Answer 2 · answered Mar 20 '19 at 11:08

-2

You may look at https://github.com/Microsoft/TypeScript/issues/212

Seems that even MS doesn't know how to make bind, call and apply strongly typed

answered Mar 20 '19 at 11:08

Fyodor Yemelyanenko

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The issue is marked as fixed and references the PR I reference in my answer. It is now possible since 3.2 (Please delete the answer as is factually incorrect) – Titian Cernicova-Dragomir Mar 20 '19 at 11:09

Enforce typings when using bind

2 Answers2