callapply 的模拟实现

Posted 2022-09-10 izyk

1. call的模拟实现

Function.prototype.myCall = function (context = window, ...args) 
  context = context || window  // 如果没有context参数，就返回window
    
  if (this === Function.prototype) 
    return undefined  // 直接调用Function.prorotype.myCall() 反回undefined       
  

  fn = Symbol()
  context[fn] = this  // 为context设置Symbol属性，并将当前函数赋给该属性
  const result = context[fn](...args)  // 将参数传入 
  delete context[fn]  // 删除该属性 
  return result         

Symbol属性特性： 唯一性，可以作为对象的属性，有静态属性Symbol.iterator

 

2. apply的模拟实现

Function.prototype.myApply = function (context = window, args) 
  context = context || window
  
  if (this === Function.prototype) 
    retrun undefined
  
  
  fn = Symbol()
  context[fn] = this

  let result
  if ( Array.isArray(args) ) 
    result = context[fn](...args)
    else 
    result = context[fn]()
  
  delete context[fn]  
  return result