Detailed explanation of steps to use JS array method

This time I will bring you a detailed explanation of the steps to use the JS array method. What are the precautions when using the JS array method? The following is a practical case, let’s take a look.

1.join

Function: Splice the array into a string by specifying characters .
Syntax: string arr.join([separator = ',']);
Parameters: separator can If omitted, defaults to a comma . If seprator is an empty string , then all elements in the array will be concatenated directly.
Return value: The concatenated string.

<script>
        var arr=[2,3,4,5];
        console.log(arr.join());//"2,3,4,5"
        console.log(arr.join(""));//"2345"
        console.log(arr.join("+"));//"2+3+4+5"
        console.log(arr);//[2,3,4,5]
</script>

2.push

Function: Add one or more elements to the end of the array.
Syntax: number arr.push(element1, ..., elementN);
Parameters: elementN, one or more elements.
Return value: The length of the new array.
Note: will modify the original array.

 <script>
        var att=[1,2,3,4];
        console.log(att.push("a","b"));//6
        console.log(att);//[1,2,3,4,"a","b"];
 </script>

3.unshift

Function: Add one or more elements to the head of the array.
Syntax: number arr.push(element1, ..., elementN);
Parameters: elementN, one or more elements.
Return value: The length of the new array.
Note: will modify the original array.

 <script>
        var att=[1,2,3,4];
        console.log(att.unshift("a","b"));//6
        console.log(att);//["a","b",1,2,3,4];
 </script>

4.pop

Function: DeletearrayLast a element.
Syntax: mixed arr.pop();
Return value: The deleted element.
Note: will modify the original array.

<script>
    var arr=[1,2,3,4];
    console.log(arr.pop());//4
    console.log(arr);//[1,2,3]
</script>

5.shift

Function: Delete the first element of the array. Syntax:
mixed arr.pop();Return value:
The deleted element. Note:
will modify the original array.

<script>
    var arr=[1,2,3,4];
    console.log(arr.shift());//1
    console.log(arr);//[2,3,4]
</script>

6.concat

Function:

Merge the incoming array or non-array value with the original array, form a new array and return . Syntax:
array array.concat(value1, value2, ..., valueN); Parameters:
valueN refers to the array or non-array value that needs to be merged with the original array.Return value:
Merged arrayNote:
will not modify the contents of the original array.

<script>
        var att=[1,2,3];
        var attO=["a","b"];
        var attT=[5,true];
        console.log(att.concat(10,attO,attT));//[1,2,3,10,"a","b",5,tru]
        console.log(att);//[1,2,3]
</script>

7.reverse

Function:

Reverse the position of the elements in the array.Syntax: array arr.reverse( )
Return value:
The array after reversing the orderNote:
willchange the original array.

<script>
    var arr = [1,2,3,6,5,4];
    var res = arr.reverse();
    res.push( "a" );
    console.log( res );//[4,5,6,3,2,1,"a"]
    console.log( arr );//[4,5,6,3,2,1,"a"]
</script>

8.slice

Function:

Intercept a part of the **array and return this new array.

Syntax:
array arr.slice([begin[,end]]);Return value:
The new array of after interceptionNote:
Contains the starting position, does not include includes the ending position, will not change the original array. If nothing is passed in, the original array will be array.

<script>
    var arr = ["a","b","c","d"];
//    var res = arr.slice( 1,3 );//["b","c"]
//    var res = arr.slice( 3,1 );//[]
    var res = arr.slice( -3,-1 );//["b","c"]
    var res = arr.slice();//["a","b","c","d"]
    console.log( res );
    console.log( arr );//["a","b","c","d"]
</script>

9.splice

Function:

Replace old elements with new elements to modify the contents of the array

Syntax:
array array.splice(start, deleteCount[, item1[, item2[, ...]]])Parameters:

    - start    起始位置
    - deleteCount    删除长度
    - item    添加的内容

Return value: An

array composed of the deleted elements Note :
modifies the contents of the original array.

<script>
    var att="Liangzhifang".split("");
    console.log(att.splice(2,4,["a"]));//["a","n","g","z"]
    console.log(att);//["L","i",["a"],"h","i","f","a","n","g"]
</script>

10.sort

作用： 对数组的元素进行排序。
语法： array arr.sort([compareFunction]);
参数: compareFunction可选。用来指定按某种顺序进行排列的函数。如果省略，元素按照转换为的字符串的诸个字符的Unicode位点进行排序。
返回值: 排序后的数组.

<script>
    //当什么都不传入的时候，sort（）默认由小到大排列。
    var attr=[9,5,4,3,2];
    console.log(attr.sort());//[2, 3, 4, 5, 9]
    //传入function的时候，sort（）内的function返回值大于0，由小到大排列。
    var attrO=[9,5,4,3,2];
    console.log(attrO.sort(function () {
        return 1;
    }));//[2, 3, 4, 5, 9]
    //传入function的时候，sort（）内的function返回值小于或者等于0，数组序列不变。
    var attrT=[9,5,4,3,2];
    console.log(attrT.sort(function () {
        return -1;
    }));// [9, 5, 4, 3, 2]
    //由于sort内部是随机抽取两个值，我们在利用function函数的返回值，大于0的时候，交换位置。小于或者等于0的时候不变，来排序。
    //以下是由小到大排序
    var attrTh=[9,5,4,3,2];
    console.log(attrTh.sort(function (a,b) {
        return a-b;
    }));// [2, 3, 4, 5, 9]
    //以下是由大到小排序
    var attrF=[9,5,4,3,2];
    console.log(attrF.sort(function (a,b) {
        return b-a;// [9, 5, 4, 3, 2]
    }));
</script>

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