bind.ts

bind.ts

Function.prototype.bind with typings for TypeScript

Function#bind is untyped in TypeScript (in v3.0 at least, cf: #212). It always returns any.

function foo(a: number, b: number): string {
  return `${this.msg}: ${a + b}`;
}
// bar is `any`!
const bar = foo.bind({msg: 'hello'}, 10);
// ok
bar(20); // 'hello: 30'
// should be a type error, but actually allowed...
bar('anything');

bind.ts is a workaround for this issue.

import bind from 'bind.ts';

// bar is `(b: number) => string`
const bar = bind(foo, {msg: 'hello'}, 10);
// ok
bar(20); // 'hello: 30'
// error!
bar('anything');

Note: TypeScript v3.0 introduces generic rest parameters. It's helpful but cannot solve this issue completely and the type definition of Function#bind in TypeScript core is not changed.

Requirement

bind.ts v2 requires TypeScript v3.0+. For TypeScript v2.x, use bind.ts v1.

Limitation

The maximum number of params of bind() is 5.

License

MIT License: Teppei Sato <[e-mail]>