Distinguish between import and link

Title: What is the difference between import and link, specific code examples are needed

Text:
When writing web pages or programs, we often use external files or library to implement a specific functionality or style. When introducing external files, we often encounter two common methods: import and link. There are some differences in use between these two methods. Let's discuss their differences and code examples in detail.

1. import
   Import is a way to introduce external files in JavaScript. It is mainly used to introduce JavaScript files. It can be used in two ways: async and defer.

The async method is an asynchronous loading method. When the browser parses the import statement, it will not wait to download and execute the external file, but will continue to parse and execute subsequent code. This method is suitable for code that does not rely on external files for execution and can speed up page loading.

Code example:

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

The defer method is a delayed loading method. Different from async, it will wait for the page document to be loaded before executing. This ensures that external files can obtain relevant elements on the page and avoid errors.

Code example:

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

It should be noted that the import method is only suitable for introducing JavaScript files. It does not support the introduction of CSS files. It must be imported using the link tag alone.

2. link
   link is a way to introduce external files in HTML, mainly used to introduce CSS files. It has the following characteristics:

link can introduce external CSS files to apply styles to HTML documents. It can specify the path of the imported CSS file through the href attribute.

Code example:

<link rel="stylesheet" href="style.css" />

link also supports defining web icons, namely favicon. The path to the icon file can be specified through the rel="icon" and href attributes.

Code example:

<link rel="icon" href="favicon.ico" />

In addition, the link tag can specify the applicable conditions of the style file through the media attribute. For example, we can pass media="screen" to specify that the style file is only applied when the screen is displayed.

Code example:

<link rel="stylesheet" href="style.css" media="screen" />

It should be noted that the way link introduces external files is loaded synchronously, that is, the browser will download and execute the external file immediately when the link tag is parsed. This may cause the page to load slower, so consider using links carefully.

Summary:
Import and link are two commonly used ways to introduce external files, and there are some differences in their use. Import is mainly used to introduce JavaScript files, supporting asynchronous and lazy loading; while link is mainly used to introduce CSS files, supporting the definition of style conditions and web icons. In actual development, it is very important to choose the appropriate introduction method according to your own needs and scenarios.

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