1、防抖
function debounce(func, ms = 1000) {
let timer;
return function (...args) {
if (timer) {
clearTimeout(timer)
}
timer = setTimeout(() => {
func.apply(this, args)
}, ms)
}
}
// 测试
const task = () => { console.log('run task') }
const debounceTask = debounce(task, 1000)
window.addEventListener('scroll', debounceTask)
2、节流
function throttle(func, ms = 1000) {
let canRun = true
return function (...args) {
if (!canRun) return
canRun = false
setTimeout(() => {
func.apply(this, args)
canRun = true
}, ms)
}
}
// 测试
const task = () => { console.log('run task') }
const throttleTask = throttle(task, 1000)
window.addEventListener('scroll', throttleTask)
3、call
Function.prototype.myCall = function (context = globalThis) {
// 关键步骤，在 context 上调用方法，触发 this 绑定为 context，使用 Symbol 防止原有属性的覆盖
const key = Symbol('key')
context[key] = this
let args = [].slice.call(arguments, 1)
let res = context[key](...args)
delete context[key]
return res
};
// 测试
const me = { name: 'Jack' }
function say() {
console.log(`My name is ${this.name || 'default'}`);
}
say.myCall(me)
4、bind
Function.prototype.myBind = function (context = globalThis) {
const fn = this
const args = Array.from(arguments).slice(1)
const newFunc = function () {
const newArgs = args.concat(...arguments)
if (this instanceof newFunc) {
// 通过 new 调用，绑定 this 为实例对象
fn.apply(this, newArgs)
} else {
// 通过普通函数形式调用，绑定 context
fn.apply(context, newArgs)
}
}
// 支持 new 调用方式
newFunc.prototype = Object.create(fn.prototype)
return newFunc
}
// 测试
const me = { name: 'Jack' }
const other = { name: 'Jackson' }
function say() {
console.log(`My name is ${this.name || 'default'}`);
}
const meSay = say.bind(me)
meSay()
const otherSay = say.bind(other)
otherSay()
5、apply
Function.prototype.myApply = function (context = globalThis) {
// 关键步骤，在 context 上调用方法，触发 this 绑定为 context，使用 Symbol 防止原有属性的覆盖
const key = Symbol('key')
context[key] = this
let res
if (arguments[1]) {
res = context[key](...arguments[1])
} else {
res = context[key]()
}
delete context[key]
return res
}
// 测试
const me = { name: 'Jack' }
function say() {
console.log(`My name is ${this.name || 'default'}`);
}
say.myApply(me)
6、deepCopy
function deepCopy(obj, cache = new WeakMap()) {
if (!obj instanceof Object) return obj
// 防止循环引用
if (cache.get(obj)) return cache.get(obj)
// 支持函数
if (obj instanceof Function) {
return function () {
obj.apply(this, arguments)
}
}
// 支持日期
if (obj instanceof Date) return new Date(obj)
// 支持正则对象
if (obj instanceof RegExp) return new RegExp(obj.source, obj.flags)
// 还可以增加其他对象，比如：Map, Set等，根据情况判断增加即可，面试点到为止就可以了
// 数组是 key 为数字素银的特殊对象
const res = Array.isArray(obj) ? [] : {}
// 缓存 copy 的对象，用于处理循环引用的情况
cache.set(obj, res)
Object.keys(obj).forEach((key) => {
if (obj[key] instanceof Object) {
res[key] = deepCopy(obj[key], cache)
} else {
res[key] = obj[key]
}
});
return res
}
// 测试
const source = {
name: 'Jack',
meta: {
age: 12,
birth: new Date('1997-10-10'),
ary: [1, 2, { a: 1 }],
say() {
console.log('Hello');
}
}
}
source.source = source
const newObj = deepCopy(source)
console.log(newObj.meta.ary[2] === source.meta.ary[2]);
7、 观察者模式 | 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) {
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();
}
}
}
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)
setTimeout(() => {
eventBus.emit('task')
}, 1000)
8、new
function myNew(Func, ...args) {
const instance = {};
if (Func.prototype) {
Object.setPrototypeOf(instance, Func.prototype)
}
const res = Func.apply(instance, args)
if (typeof res === "function" || (typeof res === "object" && res !== null)) {
return res
}
return instance
}
// 测试
function Person(name) {
this.name = name
}
Person.prototype.sayName = function() {
console.log(`My name is ${this.name}`)
}
const me = myNew(Person, 'Jack')
me.sayName()
console.log(me)
9、promise
// 建议阅读 [Promises/A+ 标准](https://promisesaplus.com/)
class MyPromise {
constructor(func) {
this.status = 'pending'
this.value = null
this.resolvedTasks = []
this.rejectedTasks = []
this._resolve = this._resolve.bind(this)
this._reject = this._reject.bind(this)
try {
func(this._resolve, this._reject)
} catch (error) {
this._reject(error)
}
}
_resolve(value) {
setTimeout(() => {
this.status = 'fulfilled'
this.value = value
this.resolvedTasks.forEach(t => t(value))
})
}
_reject(reason) {
setTimeout(() => {
this.status = 'reject'
this.value = reason
this.rejectedTasks.forEach(t => t(reason))
})
}
then(onFulfilled, onRejected) {
return new MyPromise((resolve, reject) => {
this.resolvedTasks.push((value) => {
try {
const res = onFulfilled(value)
if (res instanceof MyPromise) {
res.then(resolve, reject)
} else {
resolve(res)
}
} catch (error) {
reject(error)
}
})
this.rejectedTasks.push((value) => {
try {
const res = onRejected(value)
if (res instanceof MyPromise) {
res.then(resolve, reject)
} else {
reject(res)
}
} catch (error) {
reject(error)
}
})
})
}
catch(onRejected) {
return this.then(null, onRejected);
}
}
// 测试
new MyPromise((resolve) => {
setTimeout(() => {
resolve(1);
}, 500);
}).then((res) => {
console.log(res);
return new MyPromise((resolve) => {
setTimeout(() => {
resolve(2);
}, 500);
});
}).then((res) => {
console.log(res);
throw new Error('a error')
}).catch((err) => {
console.log('==>', err);
})
10、图片懒加载
// <img src="default.png" data-src="https://xxxx/real.png">
function isVisible(el) {
const position = el.getBoundingClientRect()
const windowHeight = document.documentElement.clientHeight
// 顶部边缘可见
const topVisible = position.top > 0 && position.top < windowHeight;
// 底部边缘可见
const bottomVisible = position.bottom < windowHeight && position.bottom > 0;
return topVisible || bottomVisible;
}
function imageLazyLoad() {
const images = document.querySelectorAll('img')
for (let img of images) {
const realSrc = img.dataset.src
if (!realSrc) continue
if (isVisible(img)) {
img.src = realSrc
img.dataset.src = ''
}
}
}
// 测试
window.addEventListener('load', imageLazyLoad)
window.addEventListener('scroll', imageLazyLoad)
// or
window.addEventListener('scroll', throttle(imageLazyLoad, 1000))
11、数组扁平化
// 方案 1
function recursionFlat(ary = []) {
const res = []
ary.forEach(item => {
if (Array.isArray(item)) {
res.push(...recursionFlat(item))
} else {
res.push(item)
}
})
return res
}
// 方案 2
function reduceFlat(ary = []) {
return ary.reduce((res, item) => res.concat(Array.isArray(item) ? reduceFlat(item) : item), [])
}
// 测试
const source = [1, 2, [3, 4, [5, 6]], '7']
console.log(recursionFlat(source))
console.log(reduceFlat(source))
12、对象扁平化
function objectFlat(obj = {}) {
const res = {}
function flat(item, preKey = '') {
Object.entries(item).forEach(([key, val]) => {
const newKey = preKey ? `${preKey}.${key}` : key
if (val && typeof val === 'object') {
flat(val, newKey)
} else {
res[newKey] = val
}
})
}
flat(obj)
return res
}
// 测试
const source = { a: { b: { c: 1, d: 2 }, e: 3 }, f: { g: 2 } }
console.log(objectFlat(source));
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