implement Function.prototype.bind

bind.js

'use strict'

let bind = function (fn, obj) {
  return function () {
    fn.apply(obj, arguments)
  }
}


let foo = function () {
  console.log(this.a);
}

const obj = {
  a: 2
}

let bar = bind(foo, obj)

bar()
setTimeout(foo, 1000);
setTimeout(bar, 1000)