const isComplexDataType = obj => (typeof obj === 'object' || typeof obj === 'function') && obj !== null

// 实现一个简易的bind

const selfBind = function (bindTarget, ...args1) {

if (typeof this !== 'function') throw new TypeError('Bind must be called on a function')

let func = this

let boundFunc = function (...args2) {

let args = [...args1, ...args2]

// 使用new关键字调用返回新对象

if (new.target) {

let res = func.apply(this, args)

//如果构造函数返回一个对象则返回这个对象

if (isComplexDataType(res)) return res

//否则返回新建的对象

return this

} else {

func.apply(bindTarget, args)

}

}

// 绑定后的函数继承绑定前的函数(非箭头函数)

/**真正的bind创建的函数是没有prototype的,但是使用new会将创建的对象连接到bind前函数的prototype(非箭头函数)**/

this.prototype && (boundFunc.prototype = Object.create(this.prototype))

// 定义绑定后函数的长度和名字

let desc = Object.getOwnPropertyDescriptors(func)

Object.defineProperties(boundFunc, {

length: desc.length,

name: Object.assign(desc.name, {

value: `bound ${desc.name.value}`

})

})

return boundFunc

}

Function.prototype.selfBind || (Object.defineProperty(Function.prototype, 'selfBind', {

value: selfBind,

enumerable: false,

configurable: true,

writable: true

}))

function func() {

this.name = 'yeyan1996'

return {}

}

let example = {

age: 22

}

let boundFunc = func.selfBind(example)

console.dir(func)

console.dir(boundFunc)

boundFunc()

console.log(example)

let x = new boundFunc()

console.log(x)