The method of operation of the array js

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Several methods of operation of the array

Several ways to declare an array of

     字面量 声明 
     var arr = [];
     var arr = [12,3,4];
    new 一个数组
    new Array()

1. Detection is not an array,

    var arr = [12, 3];
    var o = {};
    // instanceof 检测是不是数组
    console.log(arr instanceof Array); // true
    console.log(o instanceof Array); // false
    console.log(o instanceof Object); // true   通俗点 你是不是俺的  前者属不属于后者
    // isArray()  
    console.log(Array.isArray(arr)); // true
    console.log(Array.isArray(o)); // false

2. end of the array to push one or more additional elements, modify the original returned array length is the total length of the new array

    var arr = ['red', 'green'];
    arr.push('blue', 'pink'); // 给 arr 末尾添加2个 blue pink
    var ar1 = arr.push('blue', 'pink');  // ar1    4
    console.log(arr.push('blue', 'pink')); // push 有返回值 返回的是总的长度 length
    console.log(arr); //  red  green blue 修改 原数组

3. pop () to remove one end of the array elements (can only delete one) ;; no arguments and returns the removed element

    var arr = ['pink', 'hotpink', 'deeppink'];
    arr.pop();   不需要参数
    console.log(arr.pop()); // deeppink  返回的 被删除的那个元素 值
    console.log(arr); //  ["pink", "hotpink"]

4. the unshift () to add one or more elements in front of the array, modifying the original array, returns the length of a length

    var arr = ['pink', 'hotpink', 'deeppink'];
    // arr.unshift();
    console.log(arr.unshift('yellow')); //  4
    console.log(arr);  // ["yellow", "pink", "hotpink", "deeppink"]

5. shift () removes an element in front of the array (only delete a) ;; takes no arguments, returns the removed element

    var arr = ['pink', 'hotpink', 'deeppink'];
    // arr.shift();
    console.log(arr.shift()); //  pink
    console.log(arr); // ["hotpink", "deeppink"]

6. reverse () flip, modify the original array

    var arr = ['pink', 'red', 'blue'];
    arr.reverse(); // 反转数组 修改原数组 
    console.log(arr);
    返回的结果是 : ["blue", "red", "pink"]

7. Sort sort ()

    var arr = [2, 5, 9, 1, 4];
    arr.sort(); // 无参数 按照 ascii 排列 
    console.log(arr);
    var arr = [12, 5, 9, 31, 4];
    arr.sort();
    console.log(arr); // 修改原数组
    
    
    var arr = [11, 34, 6, 9, 1];
    // arr.sort(function(){})
    // 公式
    arr.sort(function(a, b) {
       return a - b // 升序排序
    })
    console.log(arr);
    
    var arr = [11, 34, 6, 9, 1];
    // arr.sort(function(){})
    // 公式
    arr.sort(function(a, b) {
         return b - a // 降序排序
    })
    console.log(arr);

8. concat () array inside the stitching, a plurality of parameters can be

    var arr = ['red'];
    var arr1 = ['andy'];
    // console.log(arr + arr1);
    console.log(arr.concat(arr1, 'pink')); // 两个数组相连 合并成为一个数组
    输出的结果为 : ["red", "andy", "pink"] 拼接之后的数组
    console.log(arr);
    输出的结果为 : ["red"] 由于没有存变量,返回的就是原数组,也说明了,不会修改原数组

9. splice (,) remove (intercept), beginning from the first of several, a few modified to delete the original array (and POP (); and shift () as) returns the removed element

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