How to link JavaScript files in HTML pages-Front-end Q&A-php.cn

How to link JavaScript files in HTML pages

PHPz

Release： 2023-04-24 11:29:15

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JavaScript is a scripting language that can be embedded in HTML pages. In web development, we usually use JavaScript to implement some interactive functions of web pages, such as dynamically loading content, form validation, etc. When implementing these functions, we usually need to link multiple JavaScript files.

In this article, we will introduce how to link JavaScript files in HTML pages, and provide some practical experience and tips to help you better manage and maintain JavaScript code.

1. Linking JavaScript files in HTML

Linking JavaScript files in HTML is very simple, just use the <script> tag. Here is a basic example:

<!DOCTYPE html>
<html>
<head>
  <title>My Page</title>
  <script src="myscript.js"></script>
</head>
<body>
  <h1>Hello, world!</h1>
</body>
</html>

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In the above example, we used the <script> tag to link to the myscript.js file. The src attribute specifies the path to the JavaScript file. When the browser parses the HTML page, it will automatically download and execute the JavaScript file to implement related functions.

It should be noted that in order to ensure correctness and reliability, we usually recommend placing JavaScript files in the <head> tag. Because the JavaScript file may have initiated some operations before other elements have finished loading, causing errors or exceptions.

2. Use external JavaScript libraries

In actual development, we usually use some external JavaScript libraries, such as jQuery, React, Vue, etc. These libraries can help us quickly implement complex interactive effects and improve development efficiency.

If you need to link these libraries in an HTML page, you can use the <script> tag to specify the path to the library file just like linking a normal JavaScript file. For example, the jQuery library is linked as follows:

<!DOCTYPE html>
<html>
<head>
  <title>My Page</title>
  <script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
  <script src="myscript.js"></script>
</head>
<body>
  <h1>Hello, world!</h1>
</body>
</html>

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In the above example, we linked the jQuery library with our own JavaScript file. It should be noted that it is recommended to use an official CDN (Content Delivery Network) when linking to external JavaScript libraries to ensure that the library version within the CDN is the latest. It can also speed up the loading speed of library files, thereby improving the performance of web pages.

3. Link multiple JavaScript files

If you need to link multiple JavaScript files, you can use multiple <script> tags in the HTML page, each Tags are used to link a JavaScript file. For example:

<!DOCTYPE html>
<html>
<head>
  <title>My Page</title>
  <script src="jquery.min.js"></script>
  <script src="vue.min.js"></script>
  <script src="react.min.js"></script>
  <script src="myscript.js"></script>
</head>
<body>
  <h1>Hello, world!</h1>
</body>
</html>

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In the above example, we linked four JavaScript files, namely jQuery, Vue, React and our own JavaScript file. It should be noted that it is recommended to link your own JavaScript files at the end to ensure that other external libraries are loaded first to avoid loading errors or exceptions due to dependency issues.

Also, if there are dependencies between multiple JavaScript files, where one file is loaded before another, it may cause errors or exceptions. In this case, it is recommended to use packaging tools, such as Webpack, Rollup, etc., to package multiple JavaScript files into one file to avoid loading order problems.

4. Accelerate the loading speed of JavaScript files

In order to improve the performance of web pages, we usually need to shorten the loading time of JavaScript files as much as possible. The following are some practical experiences and tips to help you speed up the loading of JavaScript files:

It is recommended to use public JavaScript libraries, such as jQuery, Vue, React, etc., because these libraries are available on CDN Cache, loading speed is generally faster. For JavaScript files written by yourself, you can consider using a public CDN such as CDNJS to shorten the download time of the file.
It is recommended to place JavaScript files at the bottom of the page, because when the browser loads JavaScript files, it will block the downloading and rendering of other resources, resulting in slower page loading. Placing JavaScript files at the bottom of the page avoids this problem.
It is recommended to compress JavaScript files to reduce file size and speed up downloading. JavaScript files can be compressed using tools such as UglifyJS, Closure Compiler, etc.
It is recommended to merge JavaScript files to reduce the number of HTTP requests and thereby speed up downloads. You can use tools such as Webpack, Rollup, etc. to package multiple JavaScript files into a single file.

To sum up, linking JavaScript files is a very common and important operation in web development. We can effectively manage and maintain JavaScript code and improve web page performance and user experience by using external JavaScript libraries, linking multiple JavaScript files, accelerating the loading speed of JavaScript files, etc.

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