前端基礎(chǔ)之?dāng)?shù)組方法如joinpushpop等

前端基礎(chǔ)之?dāng)?shù)組?法如join，push，pop等數(shù)組?法?致常??法有：1.join()2.push()和pop()3.shift()和unshift()4.sort()5.reverse()6.concat()7.slice()8.splice()9.indexOf()和lastIndexOf()10.forEach()11.map()12.filter()13.every()14.some()?、join()join，就是把數(shù)組轉(zhuǎn)換成字符串，然后給他規(guī)定個(gè)連接字符，默認(rèn)的是逗號(hào)(，)書(shū)寫(xiě)格式：join("")，括號(hào)??寫(xiě)字符串(“要加引號(hào)”),vararr=[1,2,3];console.log(arr.join());//1,2,3console.log(arr.join("-"));//1-2-3console.log(arr);//[1,2,3]（原數(shù)組不變?、push()和pop()push():把??的內(nèi)容添加到數(shù)組末尾，并返回修改后的長(zhǎng)度。pop()：移除數(shù)組最后?項(xiàng)，返回移除的那個(gè)值，減少數(shù)組的length。書(shū)寫(xiě)格式：arr.push("")，括號(hào)??寫(xiě)內(nèi)容(“字符串要加引號(hào)”),書(shū)寫(xiě)格式：arr.pop()vararr=["Lily","lucy","Tom"];varcount=arr.push("Jack","Sean");console.log(count);//5console.log(arr);//["Lily","lucy","Tom","Jack","Sean"]varitem=arr.pop();console.log(item);//Seanconsole.log(arr);//["Lily","lucy","Tom","Jack"]三、shift()和unshift()shift()：刪除原數(shù)組第?項(xiàng)，并返回刪除元素的值；如果數(shù)組為空則返回undefined。unshift:將參數(shù)添加到原數(shù)組開(kāi)頭，并返回?cái)?shù)組的長(zhǎng)度。書(shū)寫(xiě)格式：arr.shift("")，括號(hào)??寫(xiě)內(nèi)容(“字符串要加引號(hào)”),vararr=["Lily","lucy","Tom"];varcount=arr.unshift("Jack","Sean");console.log(count);//5console.log(arr);//["Jack","Sean","Lily","lucy","Tom"]varitem=arr.shift();console.log(item);//Jackconsole.log(arr);//["Sean","Lily","lucy","Tom"]varaar=[];varitem=aar.shift();console.log(item);//undefined四、sort()sort()：將數(shù)組?的項(xiàng)從?到?排序書(shū)寫(xiě)格式：arr.sort()vararr1=["a","d","c","b"];console.log(arr1.sort());//["a","b","c","d"]sort()?法?較的是字符串，沒(méi)有按照數(shù)值的??對(duì)數(shù)字進(jìn)?排序，要實(shí)現(xiàn)這?點(diǎn)，就必須使??個(gè)排序函數(shù)functionsortNumber(a,b){returna-b}arr=[13,24,51,3];console.log(arr.sort());//[13,24,3,51]console.log(arr.sort(sortNumber));//[3,13,24,51](數(shù)組被改變)五、reverse()reverse()：反轉(zhuǎn)數(shù)組項(xiàng)的順序。書(shū)寫(xiě)格式：arr.reverse()vararr=[13,24,51,3];console.log(arr.reverse());//[3,51,24,13]console.log(arr);//[3,51,24,13](原數(shù)組改變)六、concat()concat()：將參數(shù)添加到原數(shù)組中。這個(gè)?法會(huì)先創(chuàng)建當(dāng)前數(shù)組?個(gè)副本，然后將接收到的參數(shù)添加到這個(gè)副本的末尾，最后返回新構(gòu)建的數(shù)組。在沒(méi)有給concat()?法傳遞參數(shù)的情況下，它只是復(fù)制當(dāng)前數(shù)組并返回副本。書(shū)寫(xiě)格式：arr.concat()，括號(hào)??寫(xiě)內(nèi)容(“字符串要加引號(hào)”)vararr=[1,3,5,7];vararrCopy=arr.concat(9,[11,13]);console.log(arrCopy);//[1,3,5,7,9,11,13]console.log(arr);//[1,3,5,原7](數(shù)組未被修改)七、slice()slice()：返回從原數(shù)組中指定開(kāi)始下標(biāo)到結(jié)束下標(biāo)之間的項(xiàng)組成的新數(shù)組。slice()?法可以接受?或兩個(gè)參數(shù)，即要返回項(xiàng)的起始和結(jié)束位置。在只有?個(gè)參數(shù)的情況下，slice()?法返回從該參數(shù)指定位置開(kāi)始到當(dāng)前數(shù)組末尾的所有項(xiàng)。如果有兩個(gè)參數(shù)，該?法返回起始和結(jié)束位置之間的項(xiàng)——但不包括結(jié)束位置的項(xiàng)。書(shū)寫(xiě)格式：arr.slice(1,3)vararr=[1,3,5,7,9,11];vararrCopy=arr.slice(1);vararrCopy2=arr.slice(1,4);vararrCopy3=arr.slice(1,-2);vararrCopy4=arr.slice(-4,-1);console.log(arr);//[1,3,5,7,9,11]()原數(shù)組沒(méi)變console.log(arrCopy);//[3,5,7,9,11]console.log(arrCopy2);//[3,5,7]console.log(arrCopy3);//[3,5,7]console.log(arrCopy4);//[5,7,9]arrCopy只設(shè)置了?個(gè)參數(shù)，也就是起始下標(biāo)為1，所以返回的數(shù)組為下標(biāo)1（包括下標(biāo)1）開(kāi)始到數(shù)組最后。arrCopy2設(shè)置了兩個(gè)參數(shù)，返回起始下標(biāo)（包括1）開(kāi)始到終?下標(biāo)（不包括4）的?數(shù)組。arrCopy3設(shè)置了兩個(gè)參數(shù)，終?下標(biāo)為負(fù)數(shù)，當(dāng)出現(xiàn)負(fù)數(shù)時(shí)，將負(fù)數(shù)加上數(shù)組長(zhǎng)度的值（6）來(lái)替換該位置的數(shù)，因此就是從1開(kāi)始到4（不包括）的?數(shù)組。arrCopy4中兩個(gè)參數(shù)都是負(fù)數(shù)，所以都加上數(shù)組長(zhǎng)度6轉(zhuǎn)換成正數(shù)，因此相當(dāng)于slice(2,5)。?、splice()splice()：刪除、插?和替換。刪除：指定2個(gè)參數(shù)：要?jiǎng)h除的第?項(xiàng)的位置和要?jiǎng)h除的項(xiàng)數(shù)。書(shū)寫(xiě)格式：arr.splice(1,3)插?：可以向指定位置插?任意數(shù)量的項(xiàng)，只需提供3個(gè)參數(shù)：起始位置、0（要?jiǎng)h除的項(xiàng)數(shù)）和要插?的項(xiàng)。書(shū)寫(xiě)格式：arr.splice(2,0,4,6)替換：可以向指定位置插?任意數(shù)量的項(xiàng)，且同時(shí)刪除任意數(shù)量的項(xiàng)，只需指定3個(gè)參數(shù)：起始位置、要?jiǎng)h除的項(xiàng)數(shù)和要插?的任意數(shù)量的項(xiàng)。插?的項(xiàng)數(shù)不必與刪除的項(xiàng)數(shù)相等。書(shū)寫(xiě)格式：arr.splice(2,0,4,6)vararr=[1,3,5,7,9,11];vararrRemoved=arr.splice(0,2);console.log(arr);//[5,7,9,11]console.log(arrRemoved);//[1,3]vararrRemoved2=arr.splice(2,0,4,6);console.log(arr);//[5,7,4,6,9,11]console.log(arrRemoved2);//[]vararrRemoved3=arr.splice(1,1,2,4);console.log(arr);//[5,2,4,4,6,9,11]console.log(arrRemoved3);//[7]九、indexOf()和lastIndexOf()indexOf()：接收兩個(gè)參數(shù)：要查找的項(xiàng)和（可選的）表?查找起點(diǎn)位置的索引。其中，從數(shù)組的開(kāi)頭（位置0）開(kāi)始向后查找。書(shū)寫(xiě)格式：arr.indexof(5)lastIndexOf：接收兩個(gè)參數(shù)：要查找的項(xiàng)和（可選的）表?查找起點(diǎn)位置的索引。其中，從數(shù)組的末尾開(kāi)始向前查找。書(shū)寫(xiě)格式：arr.lastIndexOf(5,4)vararr=[1,3,5,7,7,5,3,1];console.log(arr.indexOf(5));//2console.log(arr.lastIndexOf(5));//5console.log(arr.indexOf(5,2));//2console.log(arr.lastIndexOf(5,4));//2console.log(arr.indexOf("5"));//-1?、forEach()forEach()：對(duì)數(shù)組進(jìn)?遍歷循環(huán)，對(duì)數(shù)組中的每?項(xiàng)運(yùn)?給定函數(shù)。這個(gè)?法沒(méi)有返回值。參數(shù)都是function類(lèi)型，默認(rèn)有傳參，參數(shù)分別為：遍歷的數(shù)組內(nèi)容；第對(duì)應(yīng)的數(shù)組索引，數(shù)組本?。書(shū)寫(xiě)格式：arr.forEach()vararr=[1,2,3,4,5];arr.forEach(function(x,index,a){console.log(x+'|'+index+'|'+(a===arr));});//輸出為：//1|0|true//2|1|true//3|2|true//4|3|true//5|4|true??、map()map()：指“映射”，對(duì)數(shù)組中的每?項(xiàng)運(yùn)?給定函數(shù)，返回每次函數(shù)調(diào)?的結(jié)果組成的數(shù)組。書(shū)寫(xiě)格式：arr.map()vararr=[1,2,3,4,5];vararr2=arr.map(function(item){returnitem*item;});console.log(arr2);//[1,4,9,16,25]??、filter()filter()：“過(guò)濾”功能，數(shù)組中的每?項(xiàng)運(yùn)?給定函數(shù)，返回滿?過(guò)濾條件組成的數(shù)組。書(shū)寫(xiě)格式：arr.filter()vararr=[1,2,3,4,5,6,7,8,9,10];vararr2=arr.filter(function(x,index){returnindex%3===0||x>=8;});console.log(arr2);//[1,4,7,8,9,