Summary of array knowledge points in JavaScript

This article brings you relevant knowledge about javascript, which mainly organizes related issues related to DOM API knowledge cross-talk, including selecting page tags, operating page tag attributes, etc., Let’s take a look at it together, I hope it will be helpful to everyone.

[Related recommendations: javascript video tutorial, web front-end]

The concept of array

• An array is also an object. It functions similarly to our ordinary objects and is also used to store some values.
• The difference is that ordinary objects use strings as attribute names. , and use numbers as indexes when using arrays Manipulate elements
• Index: The integer starting from 0 is the index.
• The storage performance of arrays is better than that of ordinary objects. During development We often use arrays to store some data.

Create array object

Syntax 1: var array name = new Array();
When in When a numeric value is passed in the brackets, it indicates the length of the array. When a value greater than 1 is passed, it indicates adding elements to the array.

Syntax 2: var array name =[];
When a value is passed in within square brackets, elements are added to the array.

Returns Object when checking an array object using typeof.

Add elements to the array

1. Add directly

Syntax: Array name = [Element 1, Element 2...];

2. Add according to index (where to add the element)

Syntax: Array name [index] = 'element';

It is worth noting here that if elements are added according to index, the length of the array is calculated according to the maximum index added.

Reading elements in an array

Reading an array element is a return value and requires a variable to receive or output directly.
1. Read directly, that is, read the elements in the entire array.

Syntax: console.log(array name);

2. Read an element in the array.

Syntax: console.log(array name[index]);

3. When reading an element that does not exist, return undefined.

Commonly used properties and methods in arrays

1.length property

The length property can be set/returned Array length.

• Set the array length: Array name.length = length;
  When the set array length is > the original array length, excess space will be vacated.
  When the set array length is
• Return array length: array name.length;

##Additional tips: You can use the length attribute Adds element to the last position of the array.

2.cancat method

concat() method is used to connect two or more arrays .

Syntax:

array1.concat(array2,array3...);

3.join method

join() method is used to convert all elements in the array into a string.

Syntax:

Array name.join (separator, if not written, the default is comma separation);

4.pop method

pop() method is used to delete the last element of the array and return the deleted element .

Syntax:

Array name.pop();

##5.push method

push()

method adds one or more elements to the end of the array and returns the new length .

Syntax:

Array name.push(element 1, element 2...);

6.shift method

shift() method is used to delete the first element of the array and return the value of the first element .

Syntax: Array name.shift();

7.unshift method

# The

##unshift() method adds one or more elements to the beginning of the array and returns the new length .

Syntax:

Array name.unshift(element 1, element 2...);

##8.slice method

slice()

method returns selected elements from an existing array. Extracts a portion of a string and returns the extracted portion as a new string. Note: The slice() method does not change the original array.

Syntax:

Array name.slice(start,end);

The interval is closed on the left and open on the right If it is a negative number, the number from the bottom of the array Count.

##9.splice method

splice()

method is used to

add or Delete elements in array. Syntax:

Array name.splice (from which position (required), number of elements to be deleted (optional), elements to be added (optional))

##10.reverse method

reverse()

method is used for

Reverse the

order of the elements in the array. Syntax: Array name.reverse();

##11.sort method

sort() method is used to sort the elements of an array. The sort order can be alphabetical or numerical, and in ascending or descending order. The default sort order is ascending alphabetically.

Syntax: Array name.sort();

1. Sort alphabetically (ascending/descending order)

2. Sorting by numbers (from large to small/small to large) requires defining a function.

Traversal of arrays

Use a for loop to traverse the array.

Syntax:

for(var variable=0; variable

Array traversal small exercise

Add 6 objects to the array and add the adult list of people to a new in the array! !

nbsp;html>
    <meta>
    <meta>
    <meta>
    <title>Document</title>
    <script>
        function Person(name, age){
            this.name = name;
            this.age = age;
        }
        var per1 =new Person(&#39;苏凉&#39;,21);
        var per2 =new Person(&#39;小红&#39;,15);
        var per3 =new Person(&#39;小月&#39;,17);
        var per4 =new Person(&#39;小丽&#39;,19);
        var per5 =new Person(&#39;小水&#39;,20);
        var per6 =new Person(&#39;小花&#39;,5);
    
        var per_list= [per1,per2,per3,per4,per5,per6];

        function arrAdult(){
            var newArr=[];
            for(var i = 0;i<per_list.length;i++){
                var x = per_list[i];
                if(x.age<18){
                    console.log(x.name + &#39;未通过&#39;);
                }else if(x.age>=18){
                    console.log(x.name + &#39;恭喜你，通过了！&#39;);
                    newArr.push(x.name)
                }
            }
            return newArr;
        }

        var list = arrAdult();
        console.log(&#39;通过名单：&#39;+ list)
    </script>
    

Running results:

[Related recommendations:
javascript video tutorial

, web front end】

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