Array manipulation in JS

Array API

• Api:application programming Interface, application programming interface;
• JS in the object provided by the method is called the API;

instanceof

检测一个对象是否是数组;(用来对付复杂数据类型;)// 简单数据类型 typeof ;A instanceof B  // A是不是B造出来的;例：    var arr = [1,2,3];    console.log(arr instanceof Array); //arr属不属于Array类型;

Array.isarray ()

Array.isArray(参数); // 判断参数是不是数组,返回布尔值;例：    var arr = [1,2,3];    var num = 123;    console.log(Array.isArray(arr)); //true    console.log(Array.isArray(num)); //false

ToString ()

数组.toString(); // 把数组变成字符串,去除了[],内容用逗号链接;例：    var arr = ["aaa","bbb","ccc"];    console.log(arr.toString());      //返回 aaa,bbb,ccc

ValueOf ()

数组.valueOf();  //返回数组本身;   例：    var arr = ["aaa","bbb","ccc"];    console.log(arr.valueOf());      //返回数组本身  ["aaa","bbb","ccc"]

Array. Join (parameter)

数组.join(参数);  // 数组中的元素可以按照参数进行链接变成一个字符串;console.log(arr.join());    //和toString()一样用逗号链接console.log(arr.join("|")); //用参数链接console.log(arr.join("&")); //用参数链接console.log(arr.join(" ")); //如果是空格，真的用空格链接console.log(arr.join(""));  //空字符是无缝连接

Adding and removing of array elements push () and pop ()

1. 数组.push() //在数组的最末尾添加元素;2. 数组.pop()  //不需要参数;在数组的最末尾删除一项;例：    var arr = [1,2,3];    var aaa = arr.push("abc");//在数组的最末尾添加一个元素;    console.log(arr);//元素被修改了    console.log(aaa);//返回值是数组的长度;    aaa = arr.pop();//不需要参数;在数组的最末尾删除一项;    console.log(arr);//元素被修改了    console.log(aaa);//被删除的那一项

Unshift () and Shift ()

1. 数组.unshift() //在数组的最前面添加一个元素;2. 数组.shift()  //不需要参数;在数组的最前面删除一项;例：    var arr = [1,2,3];    aaa = arr.unshift("abc");//在数组的最前面添加一个元素;    console.log(arr);//元素被修改了    console.log(aaa);//返回值是数组的长度;    aaa = arr.shift();//不需要参数;在数组的最前面删除一项;    console.log(arr);//元素被修改了    console.log(aaa);//被删除的那一项

Array element sort reverse ()

reverse()   //翻转数组例:    var arr1 = [1,2,3,4,5];    var aaa = arr1.reverse(); // [5,4,3,2,1]

Sort ()

sort() // 数组中元素排序;(默认：从小到大)      //  默认：按照首个字符的Unicode编码排序;如果第一个相同那么就比较第二个...例：            var arr = [4,5,1,3,2,7,6];    var aaa =arr.sort();    console.log(aaa);          // [1, 2, 3, 4, 5, 6, 7]    console.log(aaa === arr);// true 原数组被排序了(冒泡排序)    //默认还可以排列字母;    var arr2 = ["c","e","d","a","b"];    var bbb = arr2.sort();    console.log(bbb);         // ["a", "b", "c", "d", "e"]    console.log(bbb===arr2); // true 原数组被排序了(冒泡排序)sort() //数值大小排序方法,需要借助回调函数;例：      var arr = [4,5,1,13,2,7,6];      //回调函数里面返回值如果是：参数1-参数2;升幂；   参数2-参数1;降幂；      arr.sort(function (a,b) {        return a-b; //升序        //return b-a; //降序        //return b.value-a.value; //按照元素value属性的大小排序;      });      console.log(arr); // [1, 2, 4, 5, 6, 7, 13]

Sort () Underlying principle

    var aaa = bubbleSort([1,12,3], function (a,b) {//        return a-b;//实参：array[j]-array[j+1]；        return b-a;//实参：array[j+1]-array[j]；    });    console.log(aaa);    function bubbleSort(array,fn){        //外循环控制轮数，内循环控制次数，都是元素个数-1;        for(var i=0;i<array.length-1;i++){            for(var j=0;j<array.length-1-i;j++){//次数优化，多比较一轮，少比较一次;                //满足条件交换位置;//                if(array[j]>array[j+1]){//大于升幂排序；否则降幂;                //a-b>0  和  a>b是一个意思;                //b-a>0  和  a<b是一个意思;//                if(array[j]-array[j+1]>0){//升幂排序//                if(array[j+1]-array[j]>0){//降幂排序                //把两个变量送到一个函数中;                if(fn(array[j],array[j+1])>0){                    var temp = array[j];                    array[j] = array[j+1];                    array[j+1] = temp;                }            }        }        //返回数组        return array;    }

Operation of the array element concat ()

数组1.concat(数组2); // 链接两个数组;var arr1 = [1,2,3];var arr2 = ["a","b","c"];var arr3 = arr1.concat(arr2);console.log(arr3)   //    [1, 2, 3, "a", "b", "c"]

Slice ()

数组.slice(开始索引值，结束索引值);     //数组截取;例 ：      var arr = [1, 2, 3, "a", "b", "c"];      console.log(arr.slice(3));            //从索引值为3截取到最后;["a", "b", "c"]      console.log(arr.slice(0,3));            //包左不包右;[1, 2, 3]      console.log(arr.slice(-2));            //负数是后几个;["b", "c"]      console.log(arr.slice(3,0));            //如果前面的比后面的大，那么就是[];[]      console.log(arr);                          //原数组不被修改;[1, 2, 3, "a", "b", "c"]

Splice ()

数组.splice(开始索引值，删除几个，替换内容1，替换内容2，...);  // 替换和删除;                                                      //改变原数组;返回值是被删除/替换的内容例:    var arr = [1,2,3,4,5,6,"a", "b", "c"]    arr.splice(5);        //从索引值为3截取到最后;(删除)    console.log(arr);     // [1, 2, 3, 4, 5]    arr.splice(1,2);    //(删除指定个数)从索引为1的开始删除2个    console.log(arr);   //[1, 4, 5]//替换    var arr = [1,2,3,4,5,6,"a", "b", "c"];    console.log(arr.splice(3,3,"aaa","bbb","ccc"));    //(删除指定数并替换)    console.log(arr);     // [1, 2, 3, "aaa", "bbb", "ccc", "a", "b", "c"]//    添加    arr.splice(3,0,"aaa","bbb","ccc");//(删除指定个数)//    console.log(arr);//截取或者替换之后的;   [1, 2, 3, "aaa", "bbb", "ccc", "aaa", "bbb", "ccc", "a", "b", "c"]

Indexof/lastindexof

数组.indexOf(元素);      // 给元素，查索引(从前往后)数组.lastIndexOf(元素);  // 给元素，查索引(从后往前)例：    var arr = ["a","b","c","d","c","b","b"];    console.log(arr.indexOf("b"));        // 1 查到以后立刻返回    console.log(arr.lastIndexOf("b"));    // 6 找到以后立刻返回    console.log(arr.indexOf("xxx"));    // -1;  查不到就返回-1；

Array iteration (traversal) every ()

对数组中每一项运行回调函数，如果都返回true，every返回true，如果有一项返回false，则停止遍历 every返回false；不写默认返回false像保镖失误一次，游戏结束！！！例：1.    var arr = [111,222,333,444,555];    arr.every(function (a,b,c) {        console.log(a);    //元素        console.log(b);    //索引值        console.log(c);    //数组本身;        console.log("-----");    //数组本身;        //数组中元素赋值：c[b] = 值;      a=有时候无法赋值;        return true;    });2.  //every返回一个bool值，全部是true才是true；有一个是false，结果就是false    var bool = arr.every(function (element, index, array) {        //判断：我们定义所有元素都大于200;        //if(element > 100){        if(element > 200){            return true;        }else{            return false;        }    })    alert(bool); //false

Filter ()

//   对数组中每一项运行回调函数，该函数返回结果是true的项组成的新数组//     新数组是有老数组中的元素组成的，return为ture的项;例：    var arr = [111,222,333,444,555];    var newArr = arr.filter(function (element, index, array) {        //只要是奇数，就组成数组;(数组中辨别元素)        if(element%2 === 0){            return true;        }else{            return false;        }    })    console.log(newArr); // [222, 444]

ForEach ()

// 和for循环一样；没有返回值;例：    var arr = [111,222,333,444,555];    var sum = 0;    var aaa = arr.forEach(function (element,index,array) {        console.log(element); // 输出数组中的每一个元素        console.log(index); // 数组元素对应的索引值        console.log(array); // 数组本身 [111, 222, 333, 444, 555]        sum += element; //数组中元素求和;    });    console.log(sum); // 数组元素加起来的和    console.log(aaa);//undefined；没有返回值 所以返回undefined

Map ()

//  对数组中每一项运行回调函数，返回该函数的结果组成的新数组//    return什么新数组中就有什么; 不return返回undefined; 对数组二次加工例：    var arr = [111,222,333,444,555];    var newArr = arr.map(function (element, index, array) {        if(index == 2){            return element; // 这里return了 所以下面返回的值是333        }        return element*100; // 返回的元素值都乘上100后的值    })    console.log(newArr); // [11100, 22200, 333, 44400, 55500]

Some ()

//对数组中每一项运行回调函数，如果该函数对某一项返回true，则some返回true; 像杀手，有一个成功，就胜利了！！！例：    var arr = [111,222,333,444,555];    var bool = arr.some(function (ele,i,array) {        //判断：数组中有3的倍数        if(ele%3 == 0){            return true;        }        return false;    })    alert(bool); //true ; 有一个成功就是true

Array empty

    1. arr.length = 0; // (不好，伪数组无法清空)    2. arr.splice(0); // 伪数组没有这个方法;    3. arr = [];     // 可以操作伪数组; (推荐!)// 伪数组: 就是长的像数组，但是没有数组的方法;也不能添加和删除元素;例： // arguments        fn(111,222,333);        function fn(){            arguments.length = 0; // 无法清空 返回 [1, 2, 3]           arguments.splice(0); // 会报错 arguments.splice is not a function            arguments = []; // 可以清空,返回空数组[]             console.log(arguments);        }

Array case

1. Output a string array to the form of a | split, such as "Liu Bei | Zhang Fei | guan Yu".       Use two ways to implement var arr = ["Liu Bei", "Zhang Fei", "Guan Yu"];       var separator = "|";       accumulate var str = arr[0] via for loop;       for (var i=1;i<arr.length;i++) {str + = Separator+arr[i]; } console.log (str);       Liu Bei, Zhang Fei | Guan Yu//join () can link the elements in the array into strings; Console.log (Arr.join ("|")); Liu Bei | Zhang Fei | guan Yu 2. Reverses the order of the elements of a string array. ["A", "B", "C", "D"], "D", "C", "B", "a"]. It is implemented in two ways.           Hint: The first and length-i-1 are exchanged//arrays. Reverse () method var arr = ["A", "B", "C", "D"]; Console.log (Arr.reverse ());  ["D", "C", "B", "a"]//Three kinds: 1. Forward traversal, reverse add;   2. Reverse traversal, positive add;           3. Meta-array element exchange location;               for (Var i=0;i<arr.length/2;i++) {var temp = arr[i];               Arr[i] = arr[arr.length-1-i];           Arr[arr.length-1-i] = temp; } console.log (arr); 3. Array of Wages [1500, 1200, 2000, 2100, 1800], the deletion of wages over 2000 var arr = [1500, 1200, 2000, 2100, 1800]   ;   Use filter () to form an array; return true; an array of components; var newArr = Arr.filter (function (Ele, I, array)       {//2000 above returns false;       if (ele<2000) {return true;       }else{return false;   }   }); Console.log (NEWARR); [1500, 1200, 1800]4.   ["C", "a", "Z", "a", "X", "a"] find the position of each of the occurrences of a in the array var arr = ["C", "a", "Z", "a", "X", "a"];   Traversal Array (for/while/do...while) ForEach (); Arr.foreach (function (ele, index, array) {//If the element equals "a" then output index value; if ("a" = = = Ele) {console.log (index)       ;   }}); 5. Write a method to remove duplicate elements of an array (array deduplication) var arr = ["Naruto", "Naruto", "adjuvant", "adjuvant", "Sakura", "Sakura"];       Method 1: The idea: Define a new array, traverse the old array, and judge if the new array contains no old array elements to add, otherwise do not add; var newArr = [];           Iterate over the old array Arr.foreach (function (Ele,index,array) {//detects the elements in the old array, if the new array exists it is not added, does not exist to add;           if (Newarr.indexof (ele) = = = 1) {//does not exist to add, (go to the new array to find the element index value, if 1 is not) Newarr.push (ele);       }       }); Console.log (NEWARR); ["Naruto", "adjuvant", "Sakura"]

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Array manipulation in JS