JavaScript深入之手写call、apply、bind

Function.prototype.myCall = function(context = window, ...args) {
  if(this === Function.prototype) {
    return undefined 
  }
  context = context || window
  const fn = Symbol()
  context[fn] = this
  const result = context[fn](...args)
  delete context[fn]
  return result
}

Function.prototype.myApply = function(context = window, args) {
  if(this === Function.prototype) {
    return undefined
  }
  const fn = Symbol()
  context[fn] = this
  let result
  if(Array.isArray(args)) {
    result = context[fn](args) 
  } else {
    result = context[fn] 
  }
  delete context[fn]
  return result
}

Function.prototype.myBind = function(context = window, ...args1) {
  if(this === Function.prototype) {
    throw new TypeError('Error') 
  }
  const _this = this
  return function F(...args2) {
    if(this instanceof F) {
      return new _this(...args1, ...args2) 
    }
    return _this.apply(context, args1.concat(args2))
  }
}