How to use Array objects in JavaScript-JS Tutorial-php.cn

How to use Array objects in JavaScript

不言

Release： 2021-04-20 14:30:25

Original

2988 people have browsed it

How to use the How to use Array objects in JavaScript object in JavaScript: First create a code file; then use new to create an array object; finally use the How to use Array objects in JavaScript object to process the array.

How to use Array objects in JavaScript

The operating environment of this article: windows7 system, javascript version 1.8.5, Dell G3 computer.

The array object of JavaScript is also one of the built-in functions of JavaScript. The How to use Array objects in JavaScript object is used to process arrays. When using the How to use Array objects in JavaScript object, we need to first create an array object with new.

We have already introduced how to create a built-in function in How to use the string object in JavaScriptIn this article, we will create it directly with new An How to use Array objects in JavaScript object

var family= new How to use Array objects in JavaScript（）;

Copy after login

Then let’s look at the specific example

The code is as follows

Add "Tom", "Jerry", "Soucy" and Use console.log to invoke debugging.

<!DOCTYPE html>
<html>
  <head>
   <meta charset="utf-8">
    <title>JavaScript</title>
  </head>
  <body>
    <script>
      var family= new How to use Array objects in JavaScript("Tom", "Jerry", "Soucy");
      console.log(family);
    </script>
  </body>
</html>

Copy after login

The operation effect is as follows

How to use How to use Array objects in JavaScript objects in JavaScript

Next let’s take a look at the properties and methods of the How to use Array objects in JavaScript object

Properties 1. length (Get the array length)

The code is as follows

<script>
      var family= new How to use Array objects in JavaScript("Tom", "Jerry", "Soucy");
      console.log(family.length);
    </script>

Copy after login

The running effect is as follows

How to use Array objects in JavaScript

In the family array There are three elements: Tom, Jerry, and Soucy, so it is displayed as 3.

About length and attributes

Replace the number of elements in the length attribute of the arrangement. If the number of elements after substitution is smaller than the number of elements before substitution, the elements will also be deleted.

This time, the length attribute of the arrangement of "Taro", "Jiro", and "Saburo" substitutes 2 for ""Taro", "Jiro".

Then please explain each code.

The initial value is as follows.

By assigning the number of elements to the length property of the array, if the number of elements after assignment is less than the number of elements before replacement, the element will be deleted.

At this time, ["Tom", "Jerry", "Soucy"] sets the length attribute of the array to 2, and the array becomes ["Tom", "Jerry"].

Let’s explain

The initial value is as follows.

var family = [&#39;Tom&#39;, &#39;Jerry&#39;, &#39;Soucy&#39;];

Copy after login

The length of the family array with an element of 3 is set to 2

family.length = 2;

Copy after login

At this time, the elements of the array family will Delete one and display the code of the array as follows.

 console.log(family)

Copy after login

The value of the array at this time is ['Tom', 'Jerry'].

How to use Array objects in JavaScript

This is the code to display the array element subscript at this time.

console.log(Object.keys(family));

Copy after login

The displayed result is 0, 1.

How to use Array objects in JavaScript

The code to display the current array length is as follows

console.log（family.length）;

Copy after login

The display result is 2

How to use Array objects in JavaScript

Let’s try to get the first element

We write the code as follows

console.log(family.1);

Copy after login

However, because the syntax is different, an error will occur. The following results will be displayed

How to use Array objects in JavaScript

This is to display the current second element (subscript 1) Correct syntax code.

console.log(family[1]);

Copy after login

The running result is as follows

How to use Array objects in JavaScript

This is the code to display the element with the subscript value 1, which is passed through the length of the array family The number obtained by decrementing the attribute by 1.

console.log(family[family.length - 1]);

Copy after login

The running result is the same as above

How to use Array objects in JavaScript

Methods of How to use Array objects in JavaScript object

Method 1. slice() (get array elements)

In the slice() method, you can search for the specified element by specifying the subscript.

(subscript How to use Array objects in JavaScript elements are numbered, starting from 0 and going to n...)

When retrieving elements, the subscript of the starting position and the subscript of the ending position must be specified in (). If a specific range is not specified, the last element will be retrieved starting from the first element.

Let’s look at a specific example

 <script>
      var family= new How to use Array objects in JavaScript("Tom", "Jerry", "Soucy");
      console.log(family.slice(0,2));
    </script>

Copy after login

The running results are as follows

How to use Array objects in JavaScript

slice(0,2)指的是从下标为0的元素开始到下标为2的元素前，所以运行结果是"Tom", "Jerry"。

还有需要知道的是：

如果slice（0），则显示"Tom", "Jerry", "Soucy"

如果slice（0,1），则显示"Tom"

如果slice（1），则显示"Jerry", "Soucy"

如果slice（1,2），则显示"Jerry"

如果slice（2），则显示"Soucy"

方法2. reverse()（翻转元素顺序）

代码如下

<script>
      var family= new How to use Array objects in JavaScript("Tom", "Jerry", "Soucy");
      console.log(family.reverse());
    </script>

Copy after login

运行结果如下：顺序翻转了过来

How to use Array objects in JavaScript

方法3. push()（在末尾添加新元素）

在push()中，您可以在数组末尾添加一个新元素，并在添加后获取元素数。

代码如下

<script>
  var family= new How to use Array objects in JavaScript("Tom", "Jerry", "Soucy");
  console.log(family.push("Marry", "Cindy"));
</script>

Copy after login

运行效果如下

How to use Array objects in JavaScript

元素个数从3增加到了5，如果要显示增加的元素，可以再输入以下代码

console.log(family)

Copy after login

运行结果如下

How to use Array objects in JavaScript

The above is the detailed content of How to use Array objects in JavaScript. For more information, please follow other related articles on the PHP Chinese website!