10个常见的前端手写功能，你全都会吗？

1、防抖
function debounce(fn, delay) {
let timer
return function (…args) {
if (timer) {
clearTimeout(timer)
}
timer = setTimeout(() => {
fn.apply(this, args)
}, delay)
}
}

// 测试
function task() {
console.log(‘run task’)
}
const debounceTask = debounce(task, 1000)
window.addEventListener(‘scroll’, debounceTask)
2、节流
function throttle(fn, delay) {
let last = 0 // 上次触发时间
return function (…args) {
const now = Date.now()
if (now - last > delay) {
last = now
fn.apply(this, args)
}
}
}

// 测试
function task() {
console.log(‘run task’)
}
const throttleTask = throttle(task, 1000)
window.addEventListener(‘scroll’, throttleTask)
3、深拷贝
JSON 方法
// 不支持值为undefined、函数和循环引用的情况
const cloneObj = JSON.parse(JSON.stringify(obj))
递归拷贝
function deepClone(obj, cache = new WeakMap()) {
if (obj === null || typeof obj !== ‘object’) return obj
if (obj instanceof Date) return new Date(obj)
if (obj instanceof RegExp) return new RegExp(obj)

if (cache.has(obj)) return cache.get(obj) // 如果出现循环引用，则返回缓存的对象，防止递归进入死循环
let cloneObj = new obj.constructor() // 使用对象所属的构造函数创建一个新对象
cache.set(obj, cloneObj) // 缓存对象，用于循环引用的情况

for (let key in obj) {
if (obj.hasOwnProperty(key)) {
cloneObj[key] = deepClone(obj[key], cache) // 递归拷贝
}
}
return cloneObj
}

// 测试
const obj = { name: ‘Jack’, address: { x: 100, y: 200 } }
obj.a = obj // 循环引用
const newObj = deepClone(obj)
console.log(newObj.address === obj.address) // false
4、手写 Promise
class MyPromise {
constructor(executor) {
this.status = ‘pending’ // 初始状态为等待
this.value = null // 成功的值
this.reason = null // 失败的原因
this.onFulfilledCallbacks = [] // 成功的回调函数数组
this.onRejectedCallbacks = [] // 失败的回调函数数组
let resolve = value => {
if (this.status === ‘pending’) {
this.status = ‘fulfilled’
this.value = value;
this.onFulfilledCallbacks.forEach(fn => fn()) // 调用成功的回调函数
}
}
let reject = reason => {
if (this.status === ‘pending’) {
this.status = ‘rejected’
this.reason = reason
this.onRejectedCallbacks.forEach(fn => fn()) // 调用失败的回调函数
}
};
try {
executor(resolve, reject)
} catch (err) {
reject(err)
}
}
then(onFulfilled, onRejected) {
return new MyPromise((resolve, reject) => {
if (this.status === ‘fulfilled’) {
setTimeout(() => {
const x = onFulfilled(this.value);
x instanceof MyPromise ? x.then(resolve, reject) : resolve(x)
})
}
if (this.status === ‘rejected’) {
setTimeout(() => {
const x = onRejected(this.reason)
x instanceof MyPromise ? x.then(resolve, reject) : resolve(x)
})
}
if (this.status === ‘pending’) {
this.onFulfilledCallbacks.push(() => { // 将成功的回调函数放入成功数组
setTimeout(() => {
const x = onFulfilled(this.value)
x instanceof MyPromise ? x.then(resolve, reject) : resolve(x)
})
})
this.onRejectedCallbacks.push(() => { // 将失败的回调函数放入失败数组
setTimeout(() => {
const x = onRejected(this.reason)
x instanceof MyPromise ? x.then(resolve, reject) : resolve(x)
})
})
}
})
}
}

// 测试
function p1() {
return new MyPromise((resolve, reject) => {
setTimeout(resolve, 1000, 1)
})
}
function p2() {
return new MyPromise((resolve, reject) => {
setTimeout(resolve, 1000, 2)
})
}
p1().then(res => {
console.log(res) // 1
return p2()
}).then(ret => {
console.log(ret) // 2
})
5、异步控制并发数
function limitRequest(urls = [], limit = 3) {
return new Promise((resolve, reject) => {
const len = urls.length
let count = 0

// 同时启动limit个任务
while (limit > 0) {
  start()
  limit -= 1
}

function start() {
  const url = urls.shift() // 从数组中拿取第一个任务
  if (url) {
    axios.post(url).then(res => {
      // todo
    }).catch(err => {
      // todo
    }).finally(() => {
      if (count == len - 1) {
        // 最后一个任务完成
        resolve()
      } else {
        // 完成之后，启动下一个任务
        count++
        start()
      }
    })
  }
}

})
}

// 测试
limitRequest([‘http://xxa’, ‘http://xxb’, ‘http://xxc’, ‘http://xxd’, ‘http://xxe’])
6、继承
ES5 继承（寄生组合继承）
function Parent(name) {
this.name = name
}
Parent.prototype.eat = function () {
console.log(this.name + ’ is eating’)
}

function Child(name, age) {
Parent.call(this, name)
this.age = age
}
Child.prototype = Object.create(Parent.prototype)
Child.prototype.constructor = Child

// 测试
let xm = new Child(‘xiaoming’, 12)
console.log(xm.name) // xiaoming
console.log(xm.age) // 12
xm.eat() // xiaoming is eating
ES6 继承
class Parent {
constructor(name) {
this.name = name
}
eat() {
console.log(this.name + ’ is eating’)
}
}

class Child extends Parent {
constructor(name, age) {
super(name)
this.age = age
}
}

// 测试
let xm = new Child(‘xiaoming’, 12)
console.log(xm.name) // xiaoming
console.log(xm.age) // 12
xm.eat() // xiaoming is eating
7、数组排序
sort 排序
// 对数字进行排序，简写
const arr = [3, 2, 4, 1, 5]
arr.sort((a, b) => a - b)
console.log(arr) // [1, 2, 3, 4, 5]

// 对字母进行排序，简写
const arr = [‘b’, ‘c’, ‘a’, ‘e’, ‘d’]
arr.sort()
console.log(arr) // [‘a’, ‘b’, ‘c’, ‘d’, ‘e’]
冒泡排序
function bubbleSort(arr) {
let len = arr.length
for (let i = 0; i < len - 1; i++) {
// 从第一个元素开始，比较相邻的两个元素，前者大就交换位置
for (let j = 0; j < len - 1 - i; j++) {
if (arr[j] > arr[j + 1]) {
let num = arr[j]
arr[j] = arr[j + 1]
arr[j + 1] = num
}
}
// 每次遍历结束，都能找到一个最大值，放在数组最后
}
return arr
}

//测试
console.log(bubbleSort([2, 3, 1, 5, 4])) // [1, 2, 3, 4, 5]
8、数组去重
Set 去重
const newArr = […new Set(arr)]
// 或
const newArr = Array.from(new Set(arr))
indexOf 去重
const newArr = arr.filter((item, index) => arr.indexOf(item) === index)
9、获取 url 参数
URLSearchParams 方法
// 创建一个URLSearchParams实例
const urlSearchParams = new URLSearchParams(window.location.search);
// 把键值对列表转换为一个对象
const params = Object.fromEntries(urlSearchParams.entries());
split 方法
function getParams(url) {
const res = {}
if (url.includes(‘?’)) {
const str = url.split(‘?’)[1]
const arr = str.split(‘&’)
arr.forEach(item => {
const key = item.split(‘=’)[0]
const val = item.split(‘=’)[1]
res[key] = decodeURIComponent(val) // 解码
})
}
return res
}

// 测试
const user = getParams(‘http://www.baidu.com?user=%E9%98%BF%E9%A3%9E&age=16’)
console.log(user) // { user: ‘阿飞’, age: ‘16’ }
10、发布订阅模式
class EventEmitter {
constructor() {
this.cache = {}
}

on(name, fn) {
if (this.cache[name]) {
this.cache[name].push(fn)
} else {
this.cache[name] = [fn]
}
}

off(name, fn) {
const tasks = this.cache[name]
if (tasks) {
const index = tasks.findIndex((f) => f === fn || f.callback === fn)
if (index >= 0) {
tasks.splice(index, 1)
}
}
}

emit(name, once = false) {
if (this.cache[name]) {
// 创建副本，如果回调函数内继续注册相同事件，会造成死循环
const tasks = this.cache[name].slice()
for (let fn of tasks) {
fn();
}
if (once) {
delete this.cache[name]
}
}
}
}

// 测试
const eventBus = new EventEmitter()
const task1 = () => { console.log(‘task1’); }
const task2 = () => { console.log(‘task2’); }

eventBus.on(‘task’, task1)
eventBus.on(‘task’, task2)
eventBus.off(‘task’, task1)
setTimeout(() => {
eventBus.emit(‘task’) // task2
}, 1000)
以上就是工作或求职中最常见的手写功能，你是不是全都掌握了呢，欢迎在评论区交流。如果文章对你有所帮助，不要忘了点上宝贵的一赞！
听说点赞的人运气都不差，相信来年第一个升职加薪的一定是你~😃