还在害怕手写题吗，本文可以帮你扩展并巩固自己的JS基础，顺便搞定90%的手写题。在工作中还可以对常用的需求进行手写实现，比如深拷贝、防抖节流等可以直接用于往后的项目中，提高项目开发效率。不说废话了，下面就直接上代码吧。
Function.prototype.myCall = function(context,...args){
let cxt = context || window;
//将当前被调用的方法定义在cxt.func上.(为了能以对象调用形式绑定this)
//新建一个唯一的Symbol变量避免重复
let func = Symbol()
cxt[func] = this;
args = args ? args : []
//以对象调用形式调用func,此时this指向cxt 也就是传入的需要绑定的this指向
const res = args.length > 0 ? cxt[func](...args) : cxt[func]();
//删除该方法，不然会对传入对象造成污染（添加该方法）
delete cxt[func];
return res;
}Function.prototype.myApply = function(context,args = []){
let cxt = context || window;
//将当前被调用的方法定义在cxt.func上.(为了能以对象调用形式绑定this)
//新建一个唯一的Symbol变量避免重复
let func = Symbol()
cxt[func] = this;
//以对象调用形式调用func,此时this指向cxt 也就是传入的需要绑定的this指向
const res = args.length > 0 ? cxt[func](...args) : cxt[func]();
delete cxt[func];
return res;
}需要考虑：
实现方法：
Function.prototype.myBind = function (context, ...args) {
//新建一个变量赋值为this，表示当前函数
const fn = this
//判断有没有传参进来，若为空则赋值[]
args = args ? args : []
//返回一个newFn函数，在里面调用fn
return function newFn(...newFnArgs) {
if (this instanceof newFn) {
return new fn(...args, ...newFnArgs)
}
return fn.apply(context, [...args,...newFnArgs])
}
}let name = '小王',age =17;
let obj = {
name:'小张',
age: this.age,
myFun: function(from,to){
console.log(this.name + ' 年龄 ' + this.age+'来自 '+from+'去往'+ to)
}
}
let db = {
name: '德玛',
age: 99
}
//结果
obj.myFun.myCall(db,'成都','上海'); // 德玛 年龄 99 来自 成都去往上海
obj.myFun.myApply(db,['成都','上海']); // 德玛 年龄 99 来自 成都去往上海
obj.myFun.myBind(db,'成都','上海')(); // 德玛 年龄 99 来自 成都去往上海
obj.myFun.myBind(db,['成都','上海'])(); // 德玛 年龄 99 来自 成都, 上海去往 undefinedfunction Person(obj) {
this.name = obj.name
this.age = obj.age
}
Person.prototype.add = function(value){
console.log(value)
}
var p1 = new Person({name:"番茄", age: 18})
function Person1(obj) {
Person.call(this, obj)
this.sex = obj.sex
}
// 这一步是继承的关键
Person1.prototype = Object.create(Person.prototype);
Person1.prototype.constructor = Person1;
Person1.prototype.play = function(value){
console.log(value)
}
var p2 = new Person1({name:"鸡蛋", age: 118, sex: "男"})//class 相当于es5中构造函数
//class中定义方法时，前后不能加function，全部定义在class的protopyte属性中
//class中定义的所有方法是不可枚举的
//class中只能定义方法，不能定义对象，变量等
//class和方法内默认都是严格模式
//es5中constructor为隐式属性
class People{
constructor(name='wang',age='27'){
this.name = name;
this.age = age;
}
eat(){
console.log(`${this.name} ${this.age} eat food`)
}
}
//继承父类
class Woman extends People{
constructor(name = 'ren',age = '27'){
//继承父类属性
super(name, age);
}
eat(){
//继承父类方法
super.eat()
}
}
let wonmanObj=new Woman('xiaoxiami');
wonmanObj.eat();
//es5继承先创建子类的实例对象，然后再将父类的方法添加到this上（Parent.apply(this)）。
//es6继承是使用关键字super先创建父类的实例对象this，最后在子类class中修改this。function Ctor(){
....
}
function myNew(ctor,...args){
if(typeof ctor !== 'function'){
throw 'myNew function the first param must be a function';
}
var newObj = Object.create(ctor.prototype); //创建一个继承自ctor.prototype的新对象
var ctorReturnResult = ctor.apply(newObj, args); //将构造函数ctor的this绑定到newObj中
var isObject = typeof ctorReturnResult === 'object' && ctorReturnResult !== null;
var isFunction = typeof ctorReturnResult === 'function';
if(isObject || isFunction){
return ctorReturnResult;
}
return newObj;
}
let c = myNew(Ctor);function myInstanceOf(a,b){
let left = a.__proto__;
let right = b.prototype;
while(true){
if(left == null){
return false
}
if(left == right){
return true
}
left = left.__proto__
}
}
//instanceof 运算符用于判断构造函数的 prototype 属性是否出现在对象的原型链中的任何位置。
function myInstanceof(left, right) {
let proto = Object.getPrototypeOf(left), // 获取对象的原型
prototype = right.prototype; // 获取构造函数的 prototype 对象
// 判断构造函数的 prototype 对象是否在对象的原型链上
while (true) {
if (!proto) return false;
if (proto === prototype) return true;
proto = Object.getPrototypeOf(proto);
}
}//简略版
function myCreate(obj){
// 新声明一个函数
function C(){};
// 将函数的原型指向obj
C.prototype = obj;
// 返回这个函数的实力化对象
return new C()
}
//官方版Polyfill
if (typeof Object.create !== "function") {
Object.create = function (proto, propertiesObject) {
if (typeof proto !== 'object' && typeof proto !== 'function') {
throw new TypeError('Object prototype may only be an Object: ' + proto);
} else if (proto === null) {
throw new Error("This browser's implementation of Object.create is a shim and doesn't support 'null' as the first argument.");
}
if (typeof propertiesObject !== 'undefined') throw new Error("This browser's implementation of Object.create is a shim and doesn't support a second argument.");
function F() {}
F.prototype = proto;
return new F();
};
}Object.assign2 = function(target, ...source) {
if (target == null) {
throw new TypeError('Cannot convert undefined or null to object')
}
let ret = Object(target)
source.forEach(function(obj) {
if (obj != null) {
for (let key in obj) {
if (obj.hasOwnProperty(key)) {
ret[key] = obj[key]
}
}
}
})
return ret
}实现 Promise 需要完全读懂 Promise A+ 规范，不过从总体的实现上看，有如下几个点需要考虑到：
class Promise {
callbacks = [];
state = 'pending';//增加状态
value = null;//保存结果
constructor(fn) {
fn(this._resolve.bind(this), this._reject.bind(this));
}
then(onFulfilled, onRejected) {
return new Promise((resolve, reject) => {
this._handle({
onFulfilled: onFulfilled || null,
onRejected: onRejected || null,
resolve: resolve,
reject: reject
});
});
}
_handle(callback) {
if (this.state === 'pending') {
this.callbacks.push(callback);
return;
}
let cb = this.state === 'fulfilled' ? callback.onFulfilled : callback.onRejected;
if (!cb) {//如果then中没有传递任何东西
cb = this.state === 'fulfilled' ? callback.resolve : callback.reject;
cb(this.value);
return;
}
let ret = cb(this.value);
cb = this.state === 'fulfilled' ? callback.resolve : callback.reject;
cb(ret);
}
_resolve(value) {
if (value && (typeof value === 'object' || typeof value === 'function')) {
var then = value.then;
if (typeof then === 'function') {
then.call(value, this._resolve.bind(this), this._reject.bind(this));
return;
}
}
this.state = 'fulfilled';//改变状态
this.value = value;//保存结果
this.callbacks.forEach(callback => this._handle(callback));
}
_reject(error) {
this.state = 'rejected';
this.value = error;
this.callbacks.forEach(callback => this._handle(callback));
}
}Promise.resolve(value) {
if (value && value instanceof Promise) {
return value;
} else if (value && typeof value === 'object' && typeof value.then === 'function') {
let then = value.then;
return new Promise(resolve => {
then(resolve);
});
} else if (value) {
return new Promise(resolve => resolve(value));
} else {
return new Promise(resolve => resolve());
}
}Promise.reject = function(reason) {
return new Promise((resolve, reject) => reject(reason))
}Promise.all = function(promiseArr) {
let index = 0, result = []
return new Promise((resolve, reject) => {
promiseArr.forEach((p, i) => {
Promise.resolve(p).then(val => {
index++
result[i] = val
if (index === promiseArr.length) {
resolve(result)
}
}, err => {
reject(err)
})
})
})
}Promise.race = function(promiseArr) {
return new Promise((resolve, reject) => {
promiseArr.forEach(p => {
Promise.resolve(p).then(val => {
resolve(val)
}, err => {
rejecte(err)
})
})
})
}function ajax(url,method,body,headers){
return new Promise((resolve,reject)=>{
let req = new XMLHttpRequest();
req.open(methods,url);
for(let key in headers){
req.setRequestHeader(key,headers[key])
}
req.onreadystatechange(()=>{
if(req.readystate == 4){
if(req.status >= '200' && req.status <= 300){
resolve(req.responeText)
}else{
reject(req)
}
}
})
req.send(body)
})
}let debounce = (fn,time = 1000) => {
let timeLock = null
return function (...args){
clearTimeout(timeLock)
timeLock = setTimeout(()=>{
fn(...args)
},time)
}
}let throttle = (fn,time = 1000) => {
let flag = true;
return function (...args){
if(flag){
flag = false;
setTimeout(()=>{
flag = true;
fn(...args)
},time)
}
}
}function deepClone(obj,hash = new WeakMap()){
if(obj instanceof RegExp) return new RegExp(obj);
if(obj instanceof Date) return new Date(obj);
if(obj === null || typeof obj !== 'object') return obj;
//循环引用的情况
if(hash.has(obj)){
return hash.get(obj)
}
//new 一个相应的对象
//obj为Array，相当于new Array()
//obj为Object，相当于new Object()
let constr = new obj.constructor();
hash.set(obj,constr);
for(let key in obj){
if(obj.hasOwnProperty(key)){
constr[key] = deepClone(obj[key],hash)
}
}
//考虑symbol的情况
let symbolObj = Object.getOwnPropertySymbols(obj)
for(let i=0;i<symbolObj.length;i++){
if(obj.hasOwnProperty(symbolObj[i])){
constr[symbolObj[i]] = deepClone(obj[symbolObj[i]],hash)
}
}
return constr
}let arr = [1,2,[3,4,[5,[6]]]]
console.log(arr.flat(Infinity))//flat参数为指定要提取嵌套数组的结构深度，默认值为 1//用reduce实现
function fn(arr){
return arr.reduce((prev,cur)=>{
return prev.concat(Array.isArray(cur)?fn(cur):cur)
},[])
}function sumFn(a,b,c){return a+ b + c};
let sum = curry(sumFn);
sum(2)(3)(5)//10
sum(2,3)(5)//10function curry(fn,...args){
let fnLen = fn.length,
argsLen = args.length;
//对比函数的参数和当前传入参数
//若参数不够就继续递归返回curry
//若参数够就调用函数返回相应的值
if(fnLen > argsLen){
return function(...arg2s){
return curry(fn,...args,...arg2s)
}
}else{
return fn(...args)
}
}for (var i=1; i<=5; i++) {
(function (i) {
setTimeout(() => console.log(i), 1000*i)
})(i)
}const jsonp = function (url, data) {
return new Promise((resolve, reject) => {
// 初始化url
let dataString = url.indexOf('?') === -1 ? '?' : ''
let callbackName = `jsonpCB_${Date.now()}`
url += `${dataString}callback=${callbackName}`
if (data) {
// 有请求参数，依次添加到url
for (let k in data) {
url += `${k}=${data[k]}`
}
}
let jsNode = document.createElement('script')
jsNode.src = url
// 触发callback，触发后删除js标签和绑定在window上的callback
window[callbackName] = result => {
delete window[callbackName]
document.body.removeChild(jsNode)
if (result) {
resolve(result)
} else {
reject('没有返回数据')
}
}
// js加载异常的情况
jsNode.addEventListener('error', () => {
delete window[callbackName]
document.body.removeChild(jsNode)
reject('JavaScript资源加载失败')
}, false)
// 添加js节点到document上时，开始请求
document.body.appendChild(jsNode)
})
}
jsonp('http://192.168.0.103:8081/jsonp', {
a: 1,
b: 'heiheihei'
})
.then(result => {
console.log(result)
})
.catch(err => {
console.error(err)
})class Subject{
constructor(name){
this.name = name
this.observers = []
this.state = 'XXXX'
}
// 被观察者要提供一个接受观察者的方法
attach(observer){
this.observers.push(observer)
}
// 改变被观察着的状态
setState(newState){
this.state = newState
this.observers.forEach(o=>{
o.update(newState)
})
}
}
class Observer{
constructor(name){
this.name = name
}
update(newState){
console.log(`${this.name}say:${newState}`)
}
}
// 被观察者 灯
let sub = new Subject('灯')
let mm = new Observer('小明')
let jj = new Observer('小健')
// 订阅 观察者
sub.attach(mm)
sub.attach(jj)
sub.setState('灯亮了来电了')class EventEmitter {
constructor() {
this.events = {};
}
on(event, callback) {
let callbacks = this.events[event] || [];
callbacks.push(callback);
this.events[event] = callbacks;
return this;
}
off(event, callback) {
let callbacks = this.events[event];
this.events[event] = callbacks && callbacks.filter(fn => fn !== callback);
return this;
}
emit(event, ...args) {
let callbacks = this.events[event];
callbacks.forEach(fn => {
fn(...args);
});
return this;
}
once(event, callback) {
let wrapFun = function (...args) {
callback(...args);
this.off(event, wrapFun);
};
this.on(event, wrapFun);
return this;
}
}function getRandom(min, max) {
return Math.floor(Math.random() * (max - min)) + min
}let arr = [2,3,454,34,324,32]
arr.sort(randomSort)
function randomSort(a, b) {
return Math.random() > 0.5 ? -1 : 1;
}const EventUtils = {
// 视能力分别使用dom0||dom2||IE方式 来绑定事件
// 添加事件
addEvent: function(element, type, handler) {
if (element.addEventListener) {
element.addEventListener(type, handler, false);
} else if (element.attachEvent) {
element.attachEvent("on" + type, handler);
} else {
element["on" + type] = handler;
}
},
// 移除事件
removeEvent: function(element, type, handler) {
if (element.removeEventListener) {
element.removeEventListener(type, handler, false);
} else if (element.detachEvent) {
element.detachEvent("on" + type, handler);
} else {
element["on" + type] = null;
}
},
// 获取事件目标
getTarget: function(event) {
return event.target || event.srcElement;
},
// 获取 event 对象的引用，取到事件的所有信息，确保随时能使用 event
getEvent: function(event) {
return event || window.event;
},
// 阻止事件（主要是事件冒泡，因为 IE 不支持事件捕获）
stopPropagation: function(event) {
if (event.stopPropagation) {
event.stopPropagation();
} else {
event.cancelBubble = true;
}
},
// 取消事件的默认行为
preventDefault: function(event) {
if (event.preventDefault) {
event.preventDefault();
} else {
event.returnValue = false;
}
}
};var arr = [1, 2, 3, [4, 5], [6, [7, [8]]]]
/** * 使用递归的方式处理 * wrap 内保
存结果 ret * 返回一个递归函数 **/
function wrap() {
var ret = [];
return function flat(a) {
for (var item of
a) {
if (item.constructor === Array) {
ret.concat(flat(item))
} else {
ret.push(item)
}
}
return ret
}
}
console.log(wrap()(arr));function sleep(delay) {
var start = (new Date()).getTime();
while ((new Date()).getTime() - start < delay) {
continue;
}
}
function test() {
console.log('111');
sleep(2000);
console.log('222');
}
test()//无小数点
let num1 = '1321434322222'
num1.replace(/(\d)(?=(\d{3})+$)/g,'$1,')
//有小数点
let num2 = '342243242322.3432423'
num2.replace(/(\d)(?=(\d{3})+\.)/g,'$1,')输入:
[{a:1,b:2,c:3},{b:2,c:3,a:1},{d:2,c:2}]
输出:
[{a:1,b:2,c:3},{d:2,c:2}]function objSort(obj){
let newObj = {}
//遍历对象，并将key进行排序
Object.keys(obj).sort().map(key => {
newObj[key] = obj[key]
})
//将排序好的数组转成字符串
return JSON.stringify(newObj)
}
function unique(arr){
let set = new Set();
for(let i=0;i<arr.length;i++){
let str = objSort(arr[i])
set.add(str)
}
//将数组中的字符串转回对象
arr = [...set].map(item => {
return JSON.parse(item)
})
return arr
}let url = 'http://www.domain.com/?user=anonymous&id=123&id=456&city=%E5%8C%97%E4%BA%AC&enabled';
parseParam(url)
/* 结果
{ user: 'anonymous',
id: [ 123, 456 ], // 重复出现的 key 要组装成数组，能被转成数字的就转成数字类型
city: '北京', // 中文需解码
enabled: true, // 未指定值得 key 约定为 true
}
*/function parseParam(url) {
const paramsStr = /.+\?(.+)$/.exec(url)[1]; // 将 ? 后面的字符串取出来
const paramsArr = paramsStr.split('&'); // 将字符串以 & 分割后存到数组中
let paramsObj = {};
// 将 params 存到对象中
paramsArr.forEach(param => {
if (/=/.test(param)) { // 处理有 value 的参数
let [key, val] = param.split('='); // 分割 key 和 value
val = decodeURIComponent(val); // 解码
val = /^\d+$/.test(val) ? parseFloat(val) : val; // 判断是否转为数字
if (paramsObj.hasOwnProperty(key)) { // 如果对象有 key，则添加一个值
paramsObj[key] = [].concat(paramsObj[key], val);
} else { // 如果对象没有这个 key，创建 key 并设置值
paramsObj[key] = val;
}
} else { // 处理没有 value 的参数
paramsObj[param] = true;
}
})
return paramsObj;
}let template = '我是{{name}}，年龄{{age}}，性别{{sex}}';
let data = {
name: '姓名',
age: 18
}
render(template, data); // 我是姓名，年龄18，性别undefinedfunction render(template, data) {
const reg = /\{\{(\w+)\}\}/; // 模板字符串正则
if (reg.test(template)) { // 判断模板里是否有模板字符串
const name = reg.exec(template)[1]; // 查找当前模板里第一个模板字符串的字段
template = template.replace(reg, data[name]); // 将第一个模板字符串渲染
return render(template, data); // 递归的渲染并返回渲染后的结构
}
return template; // 如果模板没有模板字符串直接返回
}var s1 = "get-element-by-id"
// 转化为 getElementByIdvar f = function(s) {
return s.replace(/-\w/g, function(x) {
return x.slice(1).toUpperCase();
})
}let str = "abcabcabcbbccccc";
let num = 0;
let char = '';
// 使其按照一定的次序排列
str = str.split('').sort().join('');
// "aaabbbbbcccccccc"
// 定义正则表达式
let re = /(\w)\1+/g;
str.replace(re,($0,$1) => {
if(num < $0.length){
num = $0.length;
char = $1;
}
});
console.log(`字符最多的是${char}，出现了${num}次`);let imgList = [...document.querySelectorAll('img')]
let length = imgList.length
const imgLazyLoad = function() {
let count = 0
return (function() {
let deleteIndexList = []
imgList.forEach((img, index) => {
let rect = img.getBoundingClientRect()
if (rect.top < window.innerHeight) {
img.src = img.dataset.src
deleteIndexList.push(index)
count++
if (count === length) {
document.removeEventListener('scroll', imgLazyLoad)
}
}
})
imgList = imgList.filter((img, index) => !deleteIndexList.includes(index))
})()
}
// 这里最好加上防抖处理
document.addEventListener('scroll', imgLazyLoad)Copyright© 2013-2020
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