共计 10241 个字符，预计需要花费 26 分钟才能阅读完成。
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. 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)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 {
// 通过一般函数模式调用，绑定 context
fn.apply(context, newArgs)
}
}
// 反对 new 调用形式
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. call
Function.prototype.myCall = function (context = globalThis) {
// 关键步骤，在 context 上调用办法，触发 this 绑定为 context，应用 Symbol 避免原有属性的笼罩
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)6. apply
Function.prototype.myApply = function (context = globalThis) {
// 关键步骤，在 context 上调用办法，触发 this 绑定为 context，应用 Symbol 避免原有属性的笼罩
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)7. deepCopy
function deepCopy(obj, cache = new WeakMap()) {if (!obj instanceof Object) return obj
// 避免循环援用
if (cache.get(obj)) return cache.get(obj)
// 反对函数
if (obj instanceof Function) {return function () {obj.apply(this, arguments)
}
}
// 反对日期
if (obj instanceof Date) return new Date(obj)
// 反对正则对象
if (obj instanceof RegExp) return new RegExp(obj.source, obj.flags)
// 还能够减少其余对象，比方：Map, Set 等，依据状况判断减少即可，面试点到为止就能够了
// 数组是 key 为数字素银的非凡对象
const res = Array.isArray(obj) ? [] : {}
// 缓存 copy 的对象，用于解决循环援用的状况
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]);8. 事件总线 | 公布订阅模式
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]) {
// 创立正本，如果回调函数内持续注册雷同事件，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]) {
// 创立正本，如果回调函数内持续注册雷同事件，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)9. 柯里化：只传递给函数一部分参数来调用它，让它返回一个函数去解决剩下的参数
function curry(func) {return function curried(...args) {
// 要害知识点：function.length 用来获取函数的形参个数
// 补充：arguments.length 获取的是实参个数
if (args.length >= func.length) {return func.apply(this, args)
}
return function (...args2) {return curried.apply(this, args.concat(args2))
}
}
}
// 测试
function sum (a, b, c) {return a + b + c}
const curriedSum = curry(sum)
console.log(curriedSum(1, 2, 3))
console.log(curriedSum(1)(2,3))
console.log(curriedSum(1)(2)(3))10. es5 实现继承
function create(proto) {function F() {}
F.prototype = proto;
return new F();}
// Parent
function Parent(name) {this.name = name}
Parent.prototype.sayName = function () {console.log(this.name)
};
// Child
function Child(age, name) {Parent.call(this, name)
this.age = age
}
Child.prototype = create(Parent.prototype)
Child.prototype.constructor = Child
Child.prototype.sayAge = function () {console.log(this.age)
}
// 测试
const child = new Child(18, 'Jack')
child.sayName()
child.sayAge()11. instanceof
function isInstanceOf(instance, klass) {
let proto = instance.__proto__
let prototype = klass.prototype
while (true) {if (proto === null) return false
if (proto === prototype) return true
proto = proto.__proto__
}
}
// 测试
class Parent {}
class Child extends Parent {}
const child = new Child()
console.log(isInstanceOf(child, Parent), isInstanceOf(child, Child), isInstanceOf(child, Array));12. 异步并发数限度
/**
* 关键点
* 1. new promise 一经创立，立刻执行
* 2. 应用 Promise.resolve().then 能够把工作加到微工作队列，避免立刻执行迭代办法
* 3. 微工作处理过程中，产生的新的微工作，会在同一事件循环内，追加到微工作队列里
* 4. 应用 race 在某个工作实现时，持续增加工作，放弃工作依照最大并发数进行执行
* 5. 工作实现后，须要从 doingTasks 中移出
*/
function limit(count, array, iterateFunc) {const tasks = []
const doingTasks = []
let i = 0
const enqueue = () => {if (i === array.length) {return Promise.resolve()
}
const task = Promise.resolve().then(() => iterateFunc(array[i++]))
tasks.push(task)
const doing = task.then(() => doingTasks.splice(doingTasks.indexOf(doing), 1))
doingTasks.push(doing)
const res = doingTasks.length >= count ? Promise.race(doingTasks) : Promise.resolve()
return res.then(enqueue)
};
return enqueue().then(() => Promise.all(tasks))
}
// test
const timeout = i => new Promise(resolve => setTimeout(() => resolve(i), i))
limit(2, [1000, 1000, 1000, 1000], timeout).then((res) => {console.log(res)
})13. 异步串行 | 异步并行
// 字节面试题，实现一个异步加法
function asyncAdd(a, b, callback) {setTimeout(function () {callback(null, a + b);
}, 500);
}
// 解决方案
// 1. promisify
const promiseAdd = (a, b) => new Promise((resolve, reject) => {asyncAdd(a, b, (err, res) => {if (err) {reject(err)
} else {resolve(res)
}
})
})
// 2. 串行解决
async function serialSum(...args) {return args.reduce((task, now) => task.then(res => promiseAdd(res, now)), Promise.resolve(0))
}
// 3. 并行处理
async function parallelSum(...args) {if (args.length === 1) return args[0]
const tasks = []
for (let i = 0; i < args.length; i += 2) {tasks.push(promiseAdd(args[i], args[i + 1] || 0))
}
const results = await Promise.all(tasks)
return parallelSum(...results)
}
// 测试
(async () => {console.log('Running...');
const res1 = await serialSum(1, 2, 3, 4, 5, 8, 9, 10, 11, 12)
console.log(res1)
const res2 = await parallelSum(1, 2, 3, 4, 5, 8, 9, 10, 11, 12)
console.log(res2)
console.log('Done');
})()14. vue reactive
// Dep module
class Dep {static stack = []
static target = null
deps = null
constructor() {this.deps = new Set()
}
depend() {if (Dep.target) {this.deps.add(Dep.target)
}
}
notify() {this.deps.forEach(w => w.update())
}
static pushTarget(t) {if (this.target) {this.stack.push(this.target)
}
this.target = t
}
static popTarget() {this.target = this.stack.pop()
}
}
// reactive
function reactive(o) {if (o && typeof o === 'object') {Object.keys(o).forEach(k => {defineReactive(o, k, o[k])
})
}
return o
}
function defineReactive(obj, k, val) {let dep = new Dep()
Object.defineProperty(obj, k, {get() {dep.depend()
return val
},
set(newVal) {
val = newVal
dep.notify()}
})
if (val && typeof val === 'object') {reactive(val)
}
}
// watcher
class Watcher {constructor(effect) {
this.effect = effect
this.update()}
update() {Dep.pushTarget(this)
this.value = this.effect()
Dep.popTarget()
return this.value
}
}
// 测试代码
const data = reactive({msg: 'aaa'})
new Watcher(() => {console.log('===> effect', data.msg);
})
setTimeout(() => {data.msg = 'hello'}, 1000)15. promise
// 倡议浏览 [Promises/A+ 规范](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);
})16. 数组扁平化
// 计划 1
function recursionFlat(ary = []) {const res = []
ary.forEach(item => {if (Array.isArray(item)) {res.push(...recursionFlat(item))
} else {res.push(item)
}
})
return res
}
// 计划 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))17. 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));18. 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))欢送一起补充 ~ Github 地址
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