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How to introduce javascript into html

WBOY
WBOYOriginal
2023-05-09 15:24:3716550browse

In the process of web development, we often need to use JavaScript to add dynamic effects and interactive functions to web pages. So, how to introduce JavaScript into HTML files? This article will introduce how to introduce JavaScript and what to pay attention to.

1. Use the script tag to introduce JavaScript

In HTML files, we can use the 3f1c4e4b6b16bbbd69b2ee476dc4f83a2cacc6d41bbb37262a98f745aa00fbf0 tag to introduce JavaScript code. The specific steps are as follows:

  1. Find the 93f0f5c25f18dab9d176bd4f6de5d30e9c3bca370b5104690d9ef395f2c5f8d1 tag in the HTML file

  2. Add 3f1c4e4b6b16bbbd69b2ee476dc4f83a< inside 93f0f5c25f18dab9d176bd4f6de5d30e /script> Tag 

    <!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title>JavaScript引入</title>
  <script src="test.js"></script> 
<!-- 引入test.js文件 -->
</head>
<body>
  <h1>Hello World!</h1>
</body>
</html>

    As shown in the above code, we can use the 3f1c4e4b6b16bbbd69b2ee476dc4f83a2cacc6d41bbb37262a98f745aa00fbf0 tag to embed JavaScript code into an HTML file, or reference the code by introducing an external js file.

Among them, we use 352b1442a1f39d4f49881b7e5087d9182cacc6d41bbb37262a98f745aa00fbf0 to introduce external JavaScript files. The test.js file is placed in the same directory as the HTML page, and its content is as follows: 

alert("Hello World!");

When the HTML file is loaded into the 3f1c4e4b6b16bbbd69b2ee476dc4f83a tag, it will automatically interpret and execute the JavaScript in the test.js file code. At this time, a dialog box with the content "Hello World" pops up.

2. Introduction to the attributes of the script tag

In the above code, we use the src attribute of the 3f1c4e4b6b16bbbd69b2ee476dc4f83a tag to reference the external JavaScript file. So, what are the other attributes of the 3f1c4e4b6b16bbbd69b2ee476dc4f83a tag? How can I use these attributes to include JavaScript? Below, we introduce some important attributes of the 3f1c4e4b6b16bbbd69b2ee476dc4f83a tag.

  1. src attribute

This attribute is used to specify the JavaScript file that needs to be linked. 

<script src="test.js"></script>

As shown in the above code, we can specify the path of the JavaScript file that needs to be imported in the src attribute.

If the path is a relative path, it is a relative path based on the location of the HTML file. When specifying the path, you need to pay attention to the correctness of the path.

  1. async attribute

This attribute is used to execute JavaScript code asynchronously without blocking the page. For example: 

<script src="test.js" async></script>

The async attribute causes the browser not to wait for the JavaScript file to be loaded before continuing to load other resources and elements in the web page, but to load the JS file after loading other resources and elements. As a result, page rendering speeds up and users can see page content faster. However, the JavaScript introduced by the async attribute will be executed after the page rendering is completed, so it may have an impact on subsequent page behavior.

  1. defer attribute

This attribute is also used to execute JavaScript code asynchronously. Unlike the async attribute, it will be displayed on the page "DOMContentLoaded" after the HTML file is parsed. JavaScript code is executed before the event. 

<script src="test.js" defer></script>

Compared with the async attribute, the defer attribute is more suitable for JavaScript that needs to rely on DOM elements, because when it is executed, all DOM elements have been loaded. Therefore, we usually add the defer attribute when introducing JavaScript files.

  1. type attribute

This attribute specifies the MIME type of the embedded or linked JavaScript code. In HTML5, the MIME type of JavaScript defaults to "text/javascript", so we generally do not need to display the specified type attribute in the 3f1c4e4b6b16bbbd69b2ee476dc4f83a tag. 

<script type="text/javascript" src="test.js"></script>

However, if you want to introduce other types of JavaScript files (such as ts files), you need to specify the corresponding file type through the type attribute.

3. Precautions for introducing JavaScript

When introducing JavaScript files, we also need to pay attention to the following points:

  1. Try to place JavaScript files together to reduce The number of HTTP requests.
  2. If you can use CDN acceleration, try to use CDN’s JavaScript files.
  3. Introduce the JavaScript file to the bottom of the page or mark it as defer or async.
  4. Don’t write JavaScript directly in the page, but introduce it into an external JS file.

In short, introducing JavaScript into HTML is very simple, just use the 3f1c4e4b6b16bbbd69b2ee476dc4f83a2cacc6d41bbb37262a98f745aa00fbf0 tag. However, in actual development, we also need to make good use of various attributes and precautions to improve performance and code quality. I hope this article can help everyone better understand and use JavaScript introduction methods in HTML.

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