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轉(zhuǎn)載自：等不到你. https://blog.csdn.net/weixin_43758603/article/details/109895826

寫(xiě)在前面

最近我終于找到了一份滿意的工作.準(zhǔn)備面試的過(guò)程中,我整理出了一些有用的筆記,這篇就是其中之一.
既然寫(xiě)好了,不妨就放在這里分享給大家.
面試通常都有現(xiàn)場(chǎng)寫(xiě)代碼的題目,我基本每次都或多或少的翻車(chē).有意思的是,每次面試結(jié)束,自己改不到五分鐘就調(diào)試出來(lái)了.
所以面試中的寫(xiě)代碼的過(guò)程,一定不能緊張,要沉住氣慢慢來(lái).只要不是系統(tǒng)自動(dòng)檢查結(jié)果,只要是面試官看著你寫(xiě),就有很大的表現(xiàn)的機(jī)會(huì),哪怕最后做不出來(lái).
我參加的最煩人的面試,是那種系統(tǒng)判定結(jié)果的面試,只要做不出來(lái),就絕對(duì)不可能通過(guò).
仔細(xì)想想,在二三十場(chǎng)面試中,很少有我完整寫(xiě)出毫無(wú)瑕疵的答案的題目,但基本也都順利通過(guò)了.
對(duì)比來(lái)看,我的同學(xué)中,答案能運(yùn)行成功但面試沒(méi)通過(guò)的也大有人在.
可以肯定的是,面試官不會(huì)只根據(jù)是否能運(yùn)行成功來(lái)評(píng)價(jià)應(yīng)聘者.
所以,只需要順著正確思路穩(wěn)穩(wěn)地做就好了,不要怕最后運(yùn)行不成功.
如果實(shí)在做不出,也一定要和面試官說(shuō)清你當(dāng)前的進(jìn)展和思路,而不是一句"我不會(huì)"就想結(jié)束問(wèn)題.
當(dāng)然,我指的只是前端這個(gè)對(duì)算法能力要求不強(qiáng)的崗位…
有一場(chǎng)百度的面試我甚至直接和面試官說(shuō),我是個(gè)偏感性的人,喜歡但是不擅長(zhǎng)做算法.都給我通過(guò)了.
總的來(lái)看,如果能完全掌握這篇文章的內(nèi)容,就足以應(yīng)付所有前端面試中的手撕代碼環(huán)節(jié)了.
來(lái)都來(lái)了,點(diǎn)個(gè)贊唄

導(dǎo)讀
關(guān)于這篇文章,有幾點(diǎn)我想先說(shuō)清楚,方便讀者更順利的學(xué)習(xí).
這篇文章不適合前端小白閱讀,需要對(duì)JS和ES6有一定了解,否則遇到一些寫(xiě)法可能不太看得懂
因?yàn)榫τ邢?我只加了較為粗略但足以幫助讀者理解的注釋,因?yàn)槎鄶?shù)題也只有幾行代碼而已.
如果遇到還不懂的地方,我認(rèn)為讀者完全可以自己去查詢文檔來(lái)了解為什么這么做,為什么使用這個(gè)函數(shù).
或者,先查詢?cè)搯?wèn)題通常的解決思路,再回來(lái)參考我的實(shí)現(xiàn)
代碼大量使用了ES6的語(yǔ)法
學(xué)習(xí)手撕代碼,不只是理解的過(guò)程,更是實(shí)踐的過(guò)程
我在完全掌握(可以默寫(xiě)出每段代碼,并講清楚每一行的作用)以下代碼的過(guò)程中,做了以下幾件事
參考別人的實(shí)現(xiàn),結(jié)合自己的思路,寫(xiě)出一個(gè)自己的版本
不斷對(duì)代碼進(jìn)行優(yōu)化
當(dāng)你嘗試去優(yōu)化一段代碼的時(shí)候,對(duì)它的理解和記憶會(huì)異常深刻
不看之前的實(shí)現(xiàn),重新自己實(shí)現(xiàn)一次
再和之前的實(shí)現(xiàn)做對(duì)比,檢查錯(cuò)誤
反復(fù)閱讀和默寫(xiě),直到可以完全正確的默寫(xiě)為之
作為一個(gè)專(zhuān)業(yè)的程序員,除了工作中的編碼,額外的無(wú)實(shí)際產(chǎn)出的練習(xí)(反復(fù)練習(xí)解決一個(gè)問(wèn)題,反復(fù)默寫(xiě)同一段代碼),也是必不可少的.
這就像歌手不可能到了舞臺(tái)上才去練習(xí)自己的聲音.他一定會(huì)在平時(shí)大量去練聲.
這就是我強(qiáng)調(diào)要反復(fù)敲代碼的原因.別想著平時(shí)只要理解,工作中再去熟能生巧.
工作不是給你練習(xí)的地方,工作是你的舞臺(tái).
下文中幾乎每一段代碼,都是我反復(fù)優(yōu)化后的結(jié)果,希望可以帶給讀者新的啟發(fā).
我把代碼大致分成了幾個(gè)專(zhuān)題,一共包含了大致30個(gè)問(wèn)題的解決方案
除了文章中的問(wèn)題,還有些我沒(méi)有提到的,都是頻率較低的問(wèn)題
關(guān)于算法題,除了排序和查找我也基本沒(méi)有寫(xiě).因?yàn)樗惴▎?wèn)題千變?nèi)f化,需要的是解決問(wèn)題的思維,而不是固定的實(shí)現(xiàn)
重要性與順序無(wú)關(guān)
有問(wèn)題可以問(wèn)我,我都會(huì)回復(fù)

DOM

事件代理

document.getElementById("father-id").onclick=function(event){
????event=event||window.event
????let?target=event.target||event.srcElement
????//可以自己打印一下event.target.nodeName,看看是什么
????if?(target.nodeName.toLowerCase()==='xxx'){
????????//事件內(nèi)容
????}
}

數(shù)組對(duì)象

扁平化

function?flatten(arr)?{
?let?result=[]
?for?(let?i=0,len=arr.length;i??if?(Array.isArray(arr[i]))?{
???result=result.concat(flatten(arr[i]))
??}?else?{
???result.push(arr[i])
??}
?}
?return?result
}

去重 - `unique()`

function?unique(arr)?{
????let?appeard=new?Set()
????return?arr.filter(item=>{
????????//創(chuàng)建一個(gè)可以唯一標(biāo)識(shí)對(duì)象的字符串id
????????let?id=item+JSON.stringify(item)
????????if?(appeard.has(id))?{
????????????return?false
????????}?else?{
????????????appeard.add(id)
????????????return?true
????????}
????})
}

拷貝

淺拷貝

function?copy(obj)?{
?let?result=Array.isArray(obj)?[]:{}
?Object.keys(obj).forEach(key=>result[key]=obj[key])
?return?result
}

otherStar={...star}

Object.assign({},star)

深拷貝

`copy()`函數(shù)實(shí)現(xiàn)

處理了循環(huán)引用和key為symbol類(lèi)型的情況

function?copy(obj,appeard=new?Map())?{
?if?(!(obj?instanceof?Object))?return?obj//如果是原始數(shù)據(jù)類(lèi)型
????if?(appeard.has(obj))?return?appeard.get(obj)//如果已經(jīng)出現(xiàn)過(guò)

????let?result=Array.isArray(obj)?[]:{}
????appeard.set(obj,result)//將新對(duì)象放入map

????//遍歷所有屬性進(jìn)行遞歸拷貝
????;[...Object.keys(obj),...Object.getOwnPropertySymbols(obj)]
?????.forEach(key=>result[key]=copy(obj[key],appeard))

????return?result
}

`JSON.stringify`

只能處理純JSON數(shù)據(jù)
有幾種情況會(huì)發(fā)生錯(cuò)誤
包含不能轉(zhuǎn)成 JSON 格式的數(shù)據(jù)
循環(huán)引用
undefined,NaN, -Infinity, Infinity 都會(huì)被轉(zhuǎn)化成null
RegExp/函數(shù)不會(huì)拷貝
new Date()會(huì)被轉(zhuǎn)成字符串

new=JSON.parse(JSON.stringify(old))

字符串

去除空格 - `trim()`

function?myTrim(str)?{
?return?str.replace(/(^\s+)|(\s+$)/g,'')//將前空格和后空格替換為空
}

function?myTrim(str)?{//記錄前后空格的個(gè)數(shù),最后對(duì)字符串進(jìn)行截取
?let?first=0,last=str.length
?for?(let?i?in?str)?{
??if?(str[i]==='?')?{
???first++
??}?else?{
???break
??}
?}
?for?(let?i=last;i>first;i--)?{
??if?(str[i]==='?')?{
???last--
??}?else?{
???break
??}
?}
?return?str.substr(first,last-first)
}

字符串全排列

廣度優(yōu)先實(shí)現(xiàn)

function?combine(str)?{//抽出一個(gè)字符s,對(duì)其余的進(jìn)行排列,將s放在每種排列開(kāi)頭
?if?(str.length===1)?return?[str]
?let?results=[]
?for?(let?i?in?str)?{
??for?(let?s?of?combine(str.slice(0,i)+str.slice(1+(+i))))?{
???results.push(str[i]+s)
??}
?}
????//可能會(huì)出現(xiàn)類(lèi)似"aa"=>[aa,aa,aa,aa]的情況,需要去重
?return?[...new?Set(results)]
}

深度優(yōu)先實(shí)現(xiàn)

function?combine(str)?{//記錄已經(jīng)使用過(guò)的字符,深度優(yōu)先訪問(wèn)所有方案
?let?result=[]
?;(function?_combine(str,path=''){
??if?(str.length===0)?return?result.push(path)
??for?(let?i?in?str)?{
???_combine(str.slice(0,i)+str.slice((+i)+1,str.length),path+str[i])
??}
?})(str)
????//可能會(huì)出現(xiàn)類(lèi)似"aa"=>[aa,aa,aa,aa]的情況,需要去重
?return?[...new?Set(result)]
}

排序和查找

插入排序

function?sort(arr)?{//原地
?for?(let?i?in?arr)?{//選一個(gè)元素
??while?(i>0&&arr[i]-1])?{//向前移動(dòng)到合適的位置
???[arr[i],arr[i-1]]=[arr[i-1],arr[i]]
???i--
??}
?}
}

歸并排序

function?sort(arr)?{
?if?(arr.length===1)?return?arr

?//分成兩部分
?let?mid=Math.floor(arr.length/2)
?let?[part1,part2]=[sort(arr.slice(0,mid)),sort(arr.slice(mid))]

?//對(duì)比+合并
?let?result=[]
?while?(part1.length>0&&part2.length>0)
??result.push((part1[0]0]?part1:part2).shift())
?return?[...result,...part1,...part2]
}

快速排序

function?sort(arr)?{
?if?(arr.length<=1)?return?arr

????//選基準(zhǔn)值
?let?mid_pos=arr.length>>1
?let?mid=arr.splice(mid_pos,1)[0]

?let?left=[],right=[]

????//和基準(zhǔn)值比較,分別插入left,right數(shù)組
?arr.forEach(item=>(item<=mid?left:right).push(item))

?return?[...sort(left),mid,...sort(right)]//遞歸調(diào)用排序
}

二分查找

function?search(arr,target)?{//循環(huán)寫(xiě)法,不斷移動(dòng)左右指針,縮小范圍
?let?left=0,right=arr.length-1

?while?(left<=right)?{
??const?mid_pos=Math.floor((left+right)/2)
??const?mid_val=arr[mid_pos]

??if?(target===mid_val)?{
???return?mid_pos
??}?else?if?(target>mid_val)?{
???left=mid_pos+1
??}?else?{
???right=mid_pos-1
??}
?}
?return?-1
}

找出出現(xiàn)次數(shù)最多的元素 - `getMostItem()`

function?getMost(arr)?{
?//計(jì)數(shù)
?let?map=new?Map()
?arr.forEach(item=>{
??if?(map.has(item))?{
???map.set(item,map.get(item)+1)
??}?else?{
???map.set(item,1)
??}
?})

?//找出出現(xiàn)最多
?let?[max_vals,max_num]=[[arr[0]],map.get(arr[0])]
?map.forEach((count,item)=>{
??if?(count>max_num){
???max_vals=[item]
???max_num=count
??}?else?{
???max_vals.push(item)
??}?
?})
?return?max_vals
}

console.log(getMost(['1',?'2',?'3',?'3',?'55',?'3',?'55',?'55']))

功能函數(shù)實(shí)現(xiàn)

`setTimeout`實(shí)現(xiàn)`setInterval`

function?myInterval(fn,interval,...args)?{
?let?context=this
?setTimeout(()=>{
??fn.apply(context,args)
??myInterval(fn,interval,...args)//別忘了為它傳入?yún)?shù)
?},interval)
}


myInterval((num)=>console.log(num),500,10)

函數(shù)柯里化

function?sum(...args1){
????return?function?(...args2)?{
????????return?[...args1,...args2].reduce((p,n)=>p+n)
????}
}
console.log(sum(1,?2,?2)(7))

防抖節(jié)流

實(shí)現(xiàn)了兩個(gè)加工方法,返回一個(gè)加工后的防抖/節(jié)流函數(shù)

防抖

function?debounce(fn,delay)?{
?let?timer=null
?return?function?(){
??if?(timer)?clearTimeout(timer)
??timer=setTimeout(()=>fn.call(...arguments),delay)//別忘了為它傳入?yún)?shù)
?}
}

節(jié)流

function?throttle(fn,delay)?{
?let?flag=true
?return?function()?{
??if?(!flag)?return

??flag=false
??setTimeout(()=>{
???fn(...arguments)//別忘了為它傳入?yún)?shù)
???flag=true
??},delay)
?}
}

數(shù)據(jù)結(jié)構(gòu)

單鏈表

function?Node(element)?{//結(jié)點(diǎn)類(lèi)
?[this.element,this.next]=[element,null]
}

class?LinkList?{//鏈表類(lèi)
?constructor()?{
??this.length=0
??this.head=new?Node()
??this.tail=new?Node()
??this.head.next=this.tail
?}
?get_all()?{
??let?result=[]
??let?now=this.head
??while?(now.next!==this.tail)?{
???now=now.next
???result.push(now.element)
??}
??return?result
?}
?unshift(element)?{//開(kāi)頭添加
??let?node=new?Node(element)
??node.next=this.head.next
??this.head.next=node
?}
?shift(){//開(kāi)頭刪除
??let?node=this.head.next
??this.head.next=this.head.next.next
??return?node.element
?}
}
let?list=new?LinkList()
list.unshift(15)
list.unshift(16)
list.unshift(17)
console.log(list.shift())//17
console.log(list.get_all())//[?16,?15?]

設(shè)計(jì)模式

發(fā)布訂閱模式

class?Observer?{
?constructor()?{
??this.events={}//事件中心
?}
?publish(eventName,...args)?{//發(fā)布=>調(diào)用事件中心中對(duì)應(yīng)的函數(shù)
??if?(this.events[eventName])
???this.events[eventName].forEach(cb=>cb.apply(this,args))
?}
?subscribe(eventName,callback)?{//訂閱=>向事件中心中添加事件
??if?(this.events[eventName])?{
???this.events[eventName].push(callback)
??}?else?{
???this.events[eventName]=[callback]
??}
?}
?unSubscribe(eventName,callback)?{//取消訂閱
??if?(events[eventName])
???events[eventName]=events[eventName].filter(cb=>cb!==callback)
?}
}

JS原生API實(shí)現(xiàn)

`bind()` `call()` `apply()`

`apply()`

Function.prototype.myApply=function(context,args)?{
?context.fn=this//為context設(shè)置函數(shù)屬性
?let?result=context.fn(...args)//調(diào)用函數(shù)
?delete?context.fn//刪除context的函數(shù)屬性
?return?result
}

`call()`

//除了...args
//和apply都一樣
Function.prototype.myCall=function(context,...args)?{
?context.fn=this
?let?result=context.fn(...args)
?delete?context.fn
?return?result
}

`bind()`

Function.prototype.myBind=function(context,args1)?{//使用[閉包+apply]實(shí)現(xiàn)
?return?(...args2)=>this.apply(context,[...args1,...args2]);
}

`InstanceOf`

function?myInstanceOf(son,father)?{//沿著父親的原型鏈向上查找是否有兒子的原型
?while?(true)?{
??son=son.__proto__
??if?(!son)?return?false
??if?(son===father.prototype)?return?true
?}
}

myInstanceOf([],?Array)??//?true

`new`

function?myNew(constructor_fn,...args)?{
?//構(gòu)造新的空對(duì)象
?let?new_obj={}
?new_obj.__proto__=constructor_fn.prototype

?let?result=constructor_fn.apply(new_obj,args)
?//如果構(gòu)造函數(shù)沒(méi)有返回一個(gè)對(duì)象,則返回新創(chuàng)建的對(duì)象
?//如果構(gòu)造函數(shù)返回了一個(gè)對(duì)象,則返回那個(gè)對(duì)象
?//如果構(gòu)造函數(shù)返回原始值,則當(dāng)作沒(méi)有返回對(duì)象
?return?result?instanceof?Object?result:new_obj
}



function?Animal(name)?{
??this.name?=?name;
}

let?animal?=?myNew(Animal,?'dog');
console.log(animal.name)??//?dog

`reduce()` `forEach()`

`reduce()`

api用法:

arr.reduce(function(prev,?cur,?index,?arr){},?initialValue)

實(shí)現(xiàn):

Array.prototype.myReduce=function(fn,init_val){
?let?[val,idx]=init_val?[init_val,0]:[this[0],1]//設(shè)置初始值
?for?(let?i=idx,len=this.length;i??val=fn(val,this[i],i,this)//循環(huán)并迭代結(jié)果
?}
?return?val
}

console.log([1,2,3,4,5].reduce((pre,item)=>pre+item,0))?//?15

`forEach()`

api用法:

[1,3,5,7,9].myForEach(function(item,index,arr)?{
????console.log(this)
},15)

實(shí)現(xiàn):

Array.prototype.myForEach=function(fn,temp_this)?{
????for?(let?i=0,len=this.length;i????????fn.call(temp_this,this[i],i,this)//循環(huán)數(shù)組元素,為回調(diào)函數(shù)傳入?yún)?shù)
????}
}

`Promise`

`Promise.all()`

Promise.prototype.all=function(promiseList)?{
????return?new?Promise((resolve,reject)=>{
????????if?(promiseList.length===0)?return?resolve([])
????????let?result=[],count=0

????????promiseList.forEach((promise,index)=>{
????????????Promise.resolve(promise).then(value=>{
????????????????result[index]=value
????????????????if?(++count===promiseList.length)?resolve(result)
????????????},reason=>reject(reason))
????????})
????})
}

ES6所有API完整實(shí)現(xiàn)

通過(guò)Promise/A+ test測(cè)試

實(shí)現(xiàn)細(xì)節(jié)過(guò)多,還請(qǐng)參照Promise/A+規(guī)范閱讀

也可以直接參考我關(guān)于promise的筆記

深入理解promise
https://blog.csdn.net/weixin_43758603/article/details/109641486

class?Promise?{
?constructor(task)?{
??this.status="pending"
??this.value=undefined
??this.reason=undefined
??this.fulfilled_callbacks=[]
??this.rejected_callbacks=[]

??try?{
???task(this._resolve,this._reject)
??}?catch?(error)?{
???this._reject(error)
??}
?}
?then(onFulfilled,onRejected){
??if?(this.status==='fulfilled')?{
???let?promise2=new?Promise((resolve,reject)=>{
????setTimeout(()=>{
?????try?{
??????if?(!this._isFunction(onFulfilled))?{
???????resolve(this.value)
??????}?else?{
???????this._resolvePromise(promise2,onFulfilled(this.value))
??????}
?????}?catch?(error)?{
??????reject(error)
?????}
????},0)
???})
???return?promise2
??}?else?if?(this.status==='rejected')?{
???let?promise2=new?Promise((resolve,reject)=>{
????setTimeout(()=>{
?????try?{
??????if?(!this._isFunction(onRejected))?{
???????reject(this.reason)
??????}?else?{
???????this._resolvePromise(promise2,onRejected(this.reason))
??????}
?????}?catch?(error)?{
??????reject(error)
?????}
????},0)
???})
???return?promise2
??}?else?if?(this.status==='pending')??{
???let?promise2=new?Promise((resolve,reject)=>{
????this.fulfilled_callbacks.push(()=>{
?????try?{
??????if?(!this._isFunction(onFulfilled))?{
???????resolve(this.value)
??????}?else?{
???????this._resolvePromise(promise2,onFulfilled(this.value))
??????}
?????}?catch?(error)?{
??????reject(error)
?????}
????})
????this.rejected_callbacks.push(()=>{
?????try?{
??????if?(!this._isFunction(onRejected))?{
???????reject(this.reason)
??????}?else?{
???????this._resolvePromise(promise2,onRejected(this.reason))
??????}
?????}?catch?(error)?{
??????reject(error)
?????}
????})
???})
???return?promise2
??}
?}
?catch=onRejected=>this.then(null,onRejected)

?finally=onFinished=>this.then(onFinished,onFinished)

?static?deferred(){
??let?deferred={}
??deferred.promise=new?Promise((resolve,reject)=>{
???deferred.resolve=resolve
???deferred.reject=reject
??})
??return?deferred
?}
?static?resolve(value)?{
??if?(value?instanceof?Promise)?return?value
??return?new?Promise(resolve=>resolve(value))
?}
?static?reject=reason=>{return?new?Promise((resolve,?reject)=>reject(reason))}

?static?all(promiseList)?{
??return?new?Promise((resolve,reject)=>{
???if?(promiseList.length===0)?return?resolve([])
???let?result=[],count=0

???promiseList.forEach((promise,index)=>{
????Promise.resolve(promise).then(value=>{
?????result[index]=value
?????if?(++count===promiseList.length)?resolve(result)
????},reason=>reject(reason))
???})
??})
?}
?static?race(promiseList)?{
??return?new?Promise((resolve,reject)=>{
???if?(promiseList.length===0)?return?resolve()
???promiseList.forEach(promise=>{
????Promise.resolve(promise)
?????.then(value=>resolve(value),reason=>reject(reason))
???})
??})
?}
?static?allSettled(promiseList)?{
??return?new?Promise(resolve=>{
???let?result=[],count=0
???if?(len===0)?return?resolve(result)

???promiseList.forEach((promise,i)=>{
????Promise.resolve(promise).then(value=>{
?????result[i]={
??????status:'fulfilled',
??????value:value
?????}
?????if?(++count===promiseList.length)?resolve(result)
????},reason=>{
?????result[i]={
??????status:'rejected',
??????reason:reason
?????}
?????if?(++count===promiseList.length)?resolve(result)
????})
???})
??})
?}
?_resolve=value=>{
??if?(this.status!=='pending')?return
??setTimeout(()=>{
???this.status?='fulfilled'
???this.value?=?value
???this.fulfilled_callbacks.forEach(cb=>cb(this.value))
??},0)
?}
?_reject=reason=>{
??if?(this.status!=='pending')?return
??setTimeout(()=>{
???this.reason?=?reason
???this.status?='rejected'
???this.rejected_callbacks.forEach(cb=>cb(this.reason))
??},0)
?}
?_isFunction=f=>Object.prototype.toString.call(f).toLocaleLowerCase()==='[object?function]'
?
?_isObject=o=>Object.prototype.toString.call(o).toLocaleLowerCase()==='[object?object]'

?_resolvePromise(promise,x){
??if?(promise===x)?{
??????promise._reject(new?TypeError('cant?be?the?same'))
??????return
??}
??if?(x?instanceof?Promise)?{
???if?(x.status==='fulfilled')?{
????promise._resolve(x.value)
???}?else?if?(x.status==='rejected')?{
????promise._reject(x.reason)
???}?else?if?(x.status==='pending')?{
????x.then(value=>{
?????this._resolvePromise(promise,value)
????},reason=>{
?????promise._reject(reason)
????})
???}
???return
??}
??if?(this._isObject(x)||this._isFunction(x))?{
???let?then
???try?{
????then=x.then
???}?catch?(error)?{
????promise._reject(error)
????return
???}
???if?(this._isFunction(then))?{
????let?called=false
????try?{
?????then.call(x,value=>{
??????if?(called)?return
??????called=true
??????this._resolvePromise(promise,value)
?????},reason=>{
??????if?(called)?return
??????called=true
??????promise._reject(reason)
?????})
????}?catch?(error)?{
?????if?(called)?return
?????promise._reject(error)
????}
???}?else?{
????promise._resolve(x)
???}
??}?else?{
???promise._resolve(x)
??}
?}
}
module.exports?=?Promise

HTTP請(qǐng)求

AJAX封裝

function?ajax(method,url,params,callback)?{
?//對(duì)參數(shù)進(jìn)行處理
?method=method.toUpperCase()
?let?post_params=null
?let?get_params=''
?
?if?(method==='GET')?{
??if?(typeof?params==='object')?{
???let?tempArr=[]
???for?(let?key?in?params)?{
????tempArr.push(`${key}=${params[key]}`)
???}
???params=tempArr.join('&')
??}
??get_params=`?${params}`
?}?else?{
??post_params=params
?}

?//發(fā)請(qǐng)求
?let?xhr=new?XMLHttpRequest()

?xhr.onreadystatechange=function(){
??if?(xhr.readyState!==4)?return
??callback(xhr.responseText)
?}

?xhr.open(method,url+get_params,false)
?if?(method==='POST')
??xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded')

?xhr.send(post_params)?
}

ajax('get','https://www.baidu.com',{id:15},data=>console.log(data))

JSONP

function?jsonp(url,?params_obj,?callback)?{
?//創(chuàng)建一個(gè)供后端返回?cái)?shù)據(jù)調(diào)用的函數(shù)名
?let?funcName?=?'jsonp_'?+?Data.now()?+?Math.random().toString().substr(2,?5)

?//將參數(shù)拼接成字符串
?if?(typeof?params==='object')?{
??let?temp=[]
??for?(let?key?in?params)?{
???temp.push(`${key}=${params[key]}`)
??}
??params=temp.join('&')
?}

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手撕前端面試代碼題大全

寫(xiě)在前面

導(dǎo)讀

目錄

DOM

數(shù)組 對(duì)象

字符串

排序和查找

功能函數(shù)實(shí)現(xiàn)

數(shù)據(jù)結(jié)構(gòu)

設(shè)計(jì)模式

JS原生API實(shí)現(xiàn)

HTTP請(qǐng)求

DOM

事件代理

數(shù)組 對(duì)象

扁平化

去重 - unique()

拷貝

淺拷貝

深拷貝

copy()函數(shù)實(shí)現(xiàn)

JSON.stringify

字符串

去除空格 - trim()

字符串全排列

廣度優(yōu)先實(shí)現(xiàn)

深度優(yōu)先實(shí)現(xiàn)

排序和查找

插入排序

歸并排序

快速排序

二分查找

找出出現(xiàn)次數(shù)最多的元素 - getMostItem()

功能函數(shù)實(shí)現(xiàn)

setTimeout實(shí)現(xiàn)setInterval

函數(shù)柯里化

防抖 節(jié)流

防抖

節(jié)流

數(shù)據(jù)結(jié)構(gòu)

單鏈表

設(shè)計(jì)模式

發(fā)布訂閱模式

JS原生API實(shí)現(xiàn)

bind() call() apply()

apply()

call()

bind()

InstanceOf

new

reduce() forEach()

reduce()

forEach()

Promise

Promise.all()

ES6所有API完整實(shí)現(xiàn)

HTTP請(qǐng)求

AJAX封裝

JSONP

數(shù)組對(duì)象

數(shù)組對(duì)象

去重 - `unique()`

`copy()`函數(shù)實(shí)現(xiàn)

`JSON.stringify`

去除空格 - `trim()`

找出出現(xiàn)次數(shù)最多的元素 - `getMostItem()`

`setTimeout`實(shí)現(xiàn)`setInterval`

防抖節(jié)流

`bind()` `call()` `apply()`

`apply()`

`call()`

`bind()`

`InstanceOf`

`new`

`reduce()` `forEach()`

`reduce()`

`forEach()`

`Promise`

`Promise.all()`