05 bind.js

Function.prototype.myBind = function (content) {
  // 是否为函数_若不考虑参数类型可以省略
  if (typeof this !== 'function') {
    throw Error('not a function.')
  }
  // 获取参数
  let fn = this
  let args = [...arguments].slice(1)

  // 创建一个新的函数
  let resFn = function () {
    // 判断是否继承于该函数
    return fn.apply(this instanceof resFn ? this : content, [
      ...args,
      ...arguments,
    ])
  }
  // 返回一个新的函数
  return resFn
}

var module = {
  x: 42,
  getX: function () {
    return this.x
  },
}

var unboundGetX = module.getX
console.log(unboundGetX()) // The function gets invoked at the global scope
// expected output: undefined

var boundGetX = unboundGetX.myBind(module)
console.log(boundGetX())

/**
 * 面试高分版
 * @param {*} context
 * @returns
 */
Function.prototype.bind2 = function (context) {
  if (typeof context !== 'function') {
    throw new Error('Caller must be a function!')
  }

  const self = this
  const args = Array.prototype.slice.call(arguments, 1)

  const F = function () {}

  const returnFn = function () {
    const new_args = Array.prototype.slice.call(arguments)

    return self.apply(
      this instanceof returnFn ? this : context,
      args.concat(new_args),
    )
  }

  F.prototype = this.prototype

  returnFn.prototype = new F()

  return returnFn
}