手写apply,bind,call函数

Function.prototype.myCall = function(content){

  if(typeof this !== 'function'){
    throw new Error('err')
  }

  const obj = content || window
  obj.fn = this
  const args = Array.prototype.slice.myApply(arguments,[1])
  const res = obj.fn(...args)
  delete obj.fn
  return res


}


Function.prototype.myApply = function(content){

  if(typeof this !== 'function'){
    throw new Error('err')
  }

  const obj = content || window
  obj.fn = this
  const args = arguments[1] || []
  const res = obj.fn(...args)
  delete obj.fn
  return res


}


Function.prototype.myBind = function(content){

  if(typeof this !== 'function'){

    throw new Error('err')

  }

  //获取参数
  const args = Array.prototype.slice.myCall(arguments,1)

  //该this指的是调用bind函数的那个函数对象
  const self = this

  //设置一个空函数用来拷贝这个函数的原型  
  let fNop = function(){}

  let fn = function(){

    //这个函数里面的this指的是经历了fn1 = fn.bind()
    //之后生成的新的函数fn1被谁调用
    //因为new的this优先级是高于bind的，所以如果当fn1通过newfn = new fn1()
    //实例化之后，fn1将不会指向bind绑定的那个this而是指向了newfn
    //所以我们要做如下处理
    let _this =  this instanceof self ? this : content

    return self.myApply(_this, args.concat(Array.prototype.slice.myApply(arguments)))

  }

  if(this.prototype){
    fNop.prototype = this.prototype
  }

  fn.prototype = new fNop()

  return fn




}