自己实现一个call、apply、bind方法

1、call的实现

思路，js中this是根据上下文来决定的，如果是一个方法，this指向这个方法被调用的对象

//如何自己实现一个call
Function.prototype.myCall = function() {
  //obj即相当于上面的k
  var [obj, ...args] = arguments;
  console.log({arguments})
  
  //this相当于上面的a
  obj['fn'] = this;
  //获取call第二个开始的参数
  
  //相当于k.a, 即将a的this指向k
  obj['fn'](...args);

  delete obj['fn'];
}

function a(n){
  console.log(this.m, n);
}

var k = {
  m: 2
}

a.myCall(k, 1);

或

Function.prototype.myCall = function() {
    let [context, ...args] = arguments
    let funNane = Symbol('fn')
    context[funNane] = this
    context[funNane](...args)
    delete context[funNane]
}

 

2、实现一个apply

//如何自己实现一个apply
Function.prototype.myApply = function() {
  //obj即相当于上面的k
  var [obj, args] = arguments;
  console.log({arguments})
  
  //this相当于上面的a
  obj['fn'] = this;
  //获取call第二个开始的参数
  
  //相当于k.a, 即将a的this指向k
  obj['fn'](...args);

  delete obj['fn'];
}

function a(n, p){
  console.log(this.m, n, p);
}

var k = {
  m: 2
}

a.myApply(k, [1, 3]);

或

Function.prototype.myApply = function() {
    let [context, args] = arguments
    let funNane = Symbol('fn')
    context[funNane] = this
    context[funNane](...args)
    delete context[funNane]
}

 

3、实现一个bind

Function.prototype.myBind = function(object) {
    let obj = object || window;
    obj.fn = this;
    let arg = [...arguments].slice(1);
    return function() {
        obj.fn.apply(object, arg);
    }
}

或 

Function.prototype.myBind = function() {
    console.log(arguments)
    let [context, ...args] = arguments
    let funNane = Symbol('fn')
    context[funNane] = this
    return () => context[funNane](...args)
}