call、bind、apply

call

Function.prototype.myCall = function(){
  const fn = Symbol('fn');
  const [p, ...arg] = arguments;
  let undertake = p || window;
  undertake[fn] = this;
  const result = undertake[fn](...arg);
  delete undertake[fn];
  return result;
}
const o = {
  name:"张三"
}
function test(name){
  console.log(this, name)
}
test.myCall(o,'张三')

bind

Function.prototype.myBind = function(){
  const fn = Symbol("fn")
  const [p, ...arg] = arguments;
  const _o = p || window;
  _o[fn] = this;
  return function(){
    const result = _o[fn](...[...arg, ...arguments]);
    delete _o[fn];
    return result;
  }
}
const o = {
    name:"张三"
}
function test(name,age){
    console.log(this, name, age)
}
let fn = test.myBind(o,'张三')(18)

apply

Function.prototype.myApply = function(){
    const fn = Symbol('fn');
    const [p, arg] = arguments;
    const _o = p || window;
    _o[fn] = this;
    const result = _o[fn](...arg);
    delete _o[fn];
    return result;
}
const o = {
    sex:"0"
}
function test(name,age){
    console.log(this,name,age)
}
test.myApply(o,['zs',18])