手撕源码

实现 call()、apply、bind()

// call
Function.prototype.call = function call(context, ...args) {
  const self = this
  const key = Symbol('key')
  // null undefined
  context == null ? (context = window) : null
  // string number
  !/^(object|function)$/i.test(typeof context) ? (context = Object(context)) : null

  // array function object
  context[key] = self
  const result = context[key](...args)
  delete context[key]
  return result
}

// bind
Function.prototype.bind = function (context, ...args) {
  const _this = this
  return function proxy(...params) {
    return _this.apply(context, args.concat(params))
  }
}