模拟 apply/bind/call

apply

Function.prototype.myApply = function(newThis, args) { 
    Object.prototype.tmpFunc = this;
    newThis.tmpFunc(...args);
    delete Object.prototype.tmpFunc;
}

function fn1(a, b, c) {
  console.log('this', this)
  console.log(a, b, c)
}

fn1.myApply({ x: 100 }, [10, 20, 30])

bind

Function.prototype.bind1 = function () {
    const args = Array.prototype.slice.call(arguments)
    const t = args.shift()
    const self = this
    return function () {
        return self.apply(t, args)
    }
}

function fn1(a, b, c) {
    console.log('this', this)
    console.log(a, b, c)
    return 'this is fn1'
}

const fn2 = fn1.bind1({x: 100}, 10, 20, 30)
const res = fn2()
console.log(res)

call

Function.prototype.myCall = function () {
  const args = Array.prototype.slice.call(arguments);
  const newThis = args.shift();
  Object.prototype.tmpFunc = this;
  newThis.tmpFunc(...args);
  delete Object.prototype.tmpFunc;
}

function fn1(a, b, c) {
  console.log('this', this)
  console.log(a, b, c)
}

fn1.myCall({ x: 100 }, 10, 20, 30)