bind,apply,call的区别及实现

共同点

bind,apply和call都可以改变使用对象的this指向

不同点

1.bind绑定不会立即执行,需要手动调用
2.apply,call绑定函数会立即执行,如果传入的第一个参数是null,undefined则this指向window。apply和call的区别是:apply第二个参数是一个数组,而call从第二个参数起后面传入的都是单个的参数。

手写apply,call,bind

1.手写call

Function.prototype.myCall = function(context){
    context = context || window
    context.fn = this
    let args = [...arguments]
    args.shift()
    const res = context.fn(...args)
    delete context.fn
    return res 
}
//测试代码
function Apple(){}
Apple.prototype = {
    color: 'red',
    say: function(){
        console.log(`this.color is ${this.color}`)
    }
}
const banana = {
    color: 'yellow'
}
 
const apple = new Apple();
apple.say.myCall(banana) // this.color is yellow
// 传入null ,this就指向window, window.color没有值,返回undefined
apple.say.myCall(null) // this.color is undefined

2.手写apply

Function.prototype.myApply = function(context,arr){
    context = context || window
    context.fn = this
    let res = null
    if(!arr){
        res = context.fn()
    }
    let args = [...arr]
    res = context.fn(...args)
    delete context.fn
    return res 
}
//测试代码
function Apple(){}
Apple.prototype = {
    color: 'red',
    say: function(a,b){
        console.log(`this.color is ${this.color}`)
        console.log('a',a,'b',b)
    }
}
const banana = {
    color: 'yellow'
}
 
const apple = new Apple();
apple.say.myApply(banana,[1,2]) 
// this.color is yellow
// a 1 b 2
// 传入null ,this就指向window, window.color没有值,返回undefined
apple.say.myApply(banana,null) // this.color is yellow
// a undefined b undefined

3.手写bind

第一种:借助apply

Function.prototype.myBind = function(){
    const _this = this
   // 获取第一个参数,要指向的this对象
    const firstArg = Array.prototype.shift.call(arguments)
   // 获取剩余的参数
    const args = Array.prototype.slice.call(arguments)
    return function(){
        // 获取内部函数的所有参数
        const innerArg = Array.prototype.slice.call(arguments)
        const lastArg = args.concat(innerArg)
        _this.apply(firstArg,lastArg)
    }
}

第二种:不借助apply

Function.prototype.myBind = function(){
    const _this = this
    const context = Array.prototype.shift.call(arguments)
    const args = Array.prototype.slice.call(arguments)
    return function(){
        const innerArg = Array.prototype.slice.call(arguments)
        const lastArg = args.concat(innerArg)
        context.fn = _this
        const resut = context.fn(...lastArg)
        delete context.fn
        return resut
    }
}

4.实现一个new关键字

function Person(){}
function newFun(name,age){
    const newObject = new Object()
    Person.call(newObject,name,age)
    newObject.__proto__ = Person.prototype
    return newObject
}

手写节流和防抖

节流

//节流 时间戳
function throttle(fn,delay){
    let pre = 0
    return function(){
        const context = arguments
        const _this = this
        const now = +Date.now()
        if(now - pre > delay){
            fn.apply(_this,context)
            pre = now
        }
    }
}
// 节流 定时器
function throttle(fn,delay){
    let timer = null
    return function(){
        const context = arguments
        const _this = this
        if(!timer){
            timer = setTimeout(()=>{
                fn.apply(_this,context)
                timer = null
            },delay)
        }    
    }
}

防抖

function debounce(fn,delay){
    let timer = null
    return function(){
        const args = arguments
        const _this = this
        clearTimeout(timer)
        timer = setTimeout(()=>{
            fn.apply(_this,args)
            timer = null
        },delay)
            
    }
}

排序算法

1.冒泡

function bubbleSort1(arr) {
    if (arr.length < 2) {
        return arr;
    }
    // 定义 count 代表执行了趟循环
    let count = 0;
    // 冒泡排序排的趟数=数组的长度-1
    // 第一层 for 循环代表一共排序多少趟
    for (let i = 0; i < arr.length - 1; i++) {
        count++;
        let hasSort = true;
        // 第二层 for 循环代表每趟需要比较多少次 每趟比较的次数会减i,因为每趟会将最后排好一个元素,排了多少趟,则代表排好了几个元素
        for (let j = 0; j < arr.length - 1 - i; j++) {
            // 在大于的时候才会交换,等于的时候不交换,所以冒泡排序属于稳定排序算法,不会对相等两个元素执行交换
            // j=>左指针,j + 1=>右指针
            if (arr[j] > arr[j + 1]) {
                // 只要交换过,则不是有序
                hasSort = false;
                let temp = arr[j];
                arr[j] = arr[j + 1];
                arr[j + 1] = temp;
            }
        }
        if (hasSort) {
            break;
        }
    }
    console.log(`执行了${count}趟循环`);
    return arr;
}

2.快排

function qucikSort1(arr){
    if(arr.length <= 1) return arr
    const pre = arr.splice(0,1)
    let left = [],right = []
    arr.forEach(item=>{
        if(item < pre){
            left.push(item)
        }else {
          right.push(item)
        }
    })
   return qucikSort1(left).concat(pre).concat(qucikSort1(right))
}
qucikSort1([2,4,1,6]) // [1, 2, 4, 6]

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