What is the correct way to include JavaScript in html files?
Jul 04, 2025 am 12:14 AM
When introducing JavaScript correctly, you need to pay attention to the loading method and location. 1. When using the <script> tag to introduce external JS files, it should be placed before the <body> end tag or in <head> with the defer/async attribute. 2. A small amount of code can be directly embedded in the HTML <script> tag but is not recommended for large projects. 3.defer makes the script load asynchronously and execute async in order, then loads asynchronously and executes immediately suitable for independent scripts. 4 Pay attention to the application of path correctness, end tag integrity, dependency order and type="module" to ensure compatibility and correct loading. </script>
The way to properly introduce JavaScript into HTML files is actually not complicated, but there are several key points to pay attention to to ensure that the script can be loaded and executed smoothly. From the perspective of actual use, we will divide several common scenarios to explain how to correctly add JavaScript to HTML files.
1. Use the <script></script> tag to import external JS files
The most common way is to introduce an external .js file through the <script></script> tag. This method is suitable for scenarios where there is a large amount of code and requires reuse or maintenance.
<script src="main.js"></script>
A few suggestions:
- Put
<script>before the<body>end tag, so as to avoid blocking page rendering. - If you have to put the script in
<head>, consider addingdeferorasyncattributes to prevent blocking HTML parsing. - Make sure the path is correct, and be careful whether the relative and absolute paths are spelled incorrectly.
2. Embed JS code directly in HTML
If you only need a small number of scripts (such as page initialization operations), you can write them directly inside the <script> tag:
<script>
document.addEventListener("DOMContentLoaded", function () {
console.log("Page loading completed");
});
</script>Notes:
- This method is suitable for simple logic and is not recommended for large projects, which is not conducive to maintenance and caching.
- It is also recommended to place it at the bottom of
<body>, or usedeferto control the execution timing.
3. Use defer and async to control loading behavior
These two properties can significantly affect the loading and execution order of scripts, especially for performance optimization.
<script src="main.js" defer></script> <script src="analytics.js" async></script>
Distinguishing description:
-
defer: The script will be loaded asynchronously and executed in order after the HTML parsing is completed. -
async: The script is loaded asynchronously and executed immediately, with uncertain execution order, suitable for independent scripts such as statistical code.
4. Pay attention to browser compatibility and loading order
Although modern browsers generally support the standard <script> tag, it is still important to note:
- Do not miss the end tag
</script>, otherwise it may lead to parsing errors. - If there is a dependency between multiple scripts, it is best to use
deferand keep the order correct. - For modular scripts (such as ES Modules), you can use
type="module"which hasdeferbehavior by default.
<script type="module" src="app.js"></script>
Basically that's it. The key to correctly introducing JavaScript is to understand the script loading mechanism and choose the appropriate method according to your needs. It seems simple, but if you are not careful, you may cause problems such as white screen and failure of functions.
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