Summary of JavaScript array methods

This article describes the method of JavaScript array. If you don’t know the method of JavaScript array or are interested in the method of JavaScript array, then let’s take a look at this article together. Okay Stop talking nonsense and get to the point!

Test array arr = [2, 0, 1, 6];
The following methods do not affect each other's testing of arr.

shift()
Deletes and returns the first element of the array.

console.log(arr.shift());           //2
console.log(arr);                   //[1,0,6]

pop()
Removes and returns the last element of the array.

console.log(arr.pop());             //6
console.log(arr);                   //[2,0,1]

unshift(arg1, arg2, ...)
Adds one or more elements to the beginning of the array and returns the new length.
Directly modify the original array, insert the value to be added at subscript 0, and move the existing elements to higher subscripts in sequence

console.log(arr.unshift(9,3,4));    //7
console.log(arr);                   //[9,5,4,2,0,1,6]

push ( arg1, arg2, ...)
Adds one or more elements to the end of the array and returns the new length.
Modify the array directly

console.log(arr.push(9,5,4));       //7
console.log(arr);                   //[2,0,1,6,9,5,4]

concat(arr1, arr2,...)
Concatenate two or more arrays.
Returns a copy of the connected array, the original array remains unchanged

var c = [2,0];
var d = [1,5]
console.log(arr.concat(c, d));      //[2,0,1,6,2,0,1,5]
console.log(arr);                   //[2,0,1,6]

join(str)
Returns the array elements concatenated by str A String

console.log(arr.join(''));          //2016
console.log(arr);                   //[2,0,1,6]
//省略参数
console.log(arr.join());            //2,0,1,6

reverse()
Reverse the order of the elements in the array, the array structure changes, and return the array

console.log(arr.reverse());         //[6,1,0,2]
console.log(arr);                   //[6,1,0,2]

slice(start, end[excluding this element])
Returns an array selected by start, end
Negative The value represents selecting elements from the tail

console.log(arr.slice(1));          //[0,1,6]
console.log(arr);                   //[2,0,1,6]

console.log(arr.slice(0));          //[2,0,1,6]
console.log(arr.slice(-4));         //[2,0,1,6]
console.log(arr.slice(1,3));        //[0,1]
console.log(arr.slice(1,-1));       //[0,1]
console.log(arr.slice(-3,-1));      //[0,1]
console.log(arr.slice(-3,3));       //[0,1]

splice(index, deleteNum, arg1, arg2,...)
and this method It can be said to be the most comprehensive method for arrays. It can add, modify, and delete array elements.
index: The starting position of the operation (add, delete), required
delete: The number of deletions, 0 means no deletion, required Select
arg: added element (one or more), optional (for deletion, modification)
Return value: deletion operation returns an array composed of deleted elements, other operations return an empty array

//添加，向位置1添加数值1
console.log(arr.splice(1,0,1));     //[]
console.log(arr);                   //[2,1,0,1,6]

console.log(arr.splice(1,0,3,8));   //[]
console.log(arr);                   //[2,3,8,1,0,1,6]

//删除，从位置2开始删除2个数值
console.log(arr.splice(2,2));       //[8,1]
console.log(arr);                   //[2,3,0,1,6]

//修改，将位置1的数值改为9
console.log(arr.splice(1,1,9));     //[3]
console.log(arr);                   //[2,9,0,1,6]

valueOf()
w3c explanation, I don’t quite understand it yet
valueOf() method returns the original value of the Array object. This primitive value is inherited by all objects derived from the Array object. The valueOf() method is usually automatically called by JavaScript in the background and does not appear explicitly in the code.

console.log(arr.valueOf());         //[2,0,1,6]
console.log(arr);                   //[2,0,1,6]

toString()
Convert the array to a string and return the result

console.log(arr.toString());        //2,0,1,6
console.log(typeof arr.toString()); //string
console.log(arr);                   //[2,0,1,6]

toLocaleString( )
Convert the array to a local string.

console.log(arr.toLocaleString());  //2,0,1,6
console.log(arr);                   //[2,0,1,6]
//特定用法
var date = new Date();
console.log(date);                  //Thu Feb 04 2016 19:51:01 GMT+0800 (中国标准时间)
console.log(date.toLocaleString()); //2016/2/4 下午7:51:01

sort()
Without parameters, the elements in the array will be sorted alphabetically
Return the sorted array

var c = ['c','d','a'];
console.log(c.sort());          //['a','c','d']
console.log(c);                 //['a','c','d']

For the sort method, I only sorted strings above, why not numbers? You may have used digital sorting before, and you think it is okay, and it is okay. That kind of sorting sometimes occurs Question, there is a good method below, I hope to learn from it~

//升序排序
console.log(arr.sort(function(a, b){
    return a - b;
}));
console.log(arr);                 //[0,1,2,6]

//降序排序
console.log(arr.sort(function(a, b){
    return b - a;
}));
console.log(arr);                 //[6,2,1,0]

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