call、apply及bind实现原理

Function.prototype.mycall = function(context = window,...args){
  //保存被调函数到context
  context.fn = this
  //执行函数
  let result = context.fn(...args)
  //删除
  delete context.fn
  return result
}

Function.prototype.myapply = function(context = window,args){
  context = context
  //保存被调函数到context
  context.fn = this
  //执行函数
  let result = context.fn(...args)
  //删除
  delete context.fn
  return result
}

Function.prototype.mybind = function(context,...args){
  var self = this//保存被调函数
  var fbound = function(...bindArgs){
    //执行被调函数
    return self.apply(
      //判断是不是new
      this instanceof self ? this : context,
      //参数合并
      args.concat(bindArgss)
    )
  }
  fbound.prototype = Object.create(self.prototype);
  //返回待执行函数
  return fbound
}