Where to put <?script><?/script> tags in your HTML document

Where to put <script></script> tags in your HTML document

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Aabhas Saxena

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发布日期: 2024年6月20日
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The script tag is used to embed a client-side script (JavaScript) in an HTML document. The script element either contains scripting statements, or it points to an external script file through the src attribute.

The location of the script tag in the HTML document can affect the performance and behavior of the web page. There are three common places to put the script tag:

  • Inside the head element
  • At the beginning of the body element
  • At the end of the body element

Each option has its own advantages and disadvantages.


Inside the head element

Putting the script tag inside the head element means that the browser will fetch and execute the script before rendering the HTML content. This can be useful if the script needs to modify the document structure or style before it is displayed, or if the script defines functions or variables that are used by other scripts later.

However, this option also has some drawbacks:

  • It can delay the rendering of the page, since the browser has to wait for the script to download and execute before parsing the rest of the HTML.
  • It can block other resources from loading, such as images, stylesheets, or fonts, since the browser may limit the number of concurrent requests1 .
  • It can cause errors or unexpected behavior if the script tries to access or manipulate elements that are not yet defined in the HTML1 .

To avoid some of these issues, you can use the async or defer attributes on the script tag. The async attribute tells the browser to download and execute the script asynchronously, without blocking the HTML parsing. The defer attribute tells the browser to download the script but defer its execution until after the HTML is parsed. Both attributes only work for external scripts (with src attribute).

https://stackoverflow.com/questions/10808109/script-tag-async-defer

Here is an example of using a script tag inside the head element: 

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


At the beginning of the body element


Putting the script tag at the beginning of the body element means that the browser will fetch and execute the script after parsing some of the HTML content. This can be useful if the script needs to access or manipulate elements that are already defined in the HTML, or if the script does not affect the document structure or style.

However, this option also has some drawbacks:

  • It can still delay the rendering of some parts of the page, since the browser has to wait for the script to execute before parsing and displaying more HTML content.
  • It can still block other resources from loading, since the browser may limit the number of concurrent requests.
  • It can cause a flash of unstyled content (FOUC) or a flash of invisible content (FOIC) if the script modifies or hides elements that are already rendered.

To avoid some of these issues, you can use the async or defer attributes on the script tag, as explained above.

Here is an example of using a script tag at the beginning of the body element: 

<body>
<script src="script.js"></script>
<!-- rest of the HTML content -->
</body>


At the end of the body element

Putting the script tag at the end of the body element means that the browser will fetch and execute the script after parsing and rendering all of the HTML content. This can be useful if the script does not need to access or manipulate elements before they are rendered, or if the script is not essential for the functionality or appearance of the page.

This option has some advantages:

  • It can improve the perceived performance of the page, since the browser can display the HTML content faster, without waiting for the script to download and execute.
  • It can reduce the blocking of other resources from loading, since the browser can make more concurrent requests.
  • It can avoid errors or unexpected behavior if the script tries to access or manipulate elements that are already defined and rendered in the HTML.

However, this option also has some drawbacks:

  • It can delay the execution of the script, which may affect some features or interactions that depend on it.
  • It can cause a flash of unstyled content (FOUC) or a flash of invisible content (FOIC) if the script modifies or hides elements that are already rendered.

To avoid some of these issues, you can use the async or defer attributes on the script tag, as explained above.

Here is an example of using a script tag at the end of the body element: 

<body>
<!-- HTML content -->
<script src="script.js"></script>
</body>


The placement of <script> tags in an HTML document depends on the purpose of the script. Here are some guidelines:

  1. Critical Scripts (e.g., analytics, API, authentication): Place them in the head section. These scripts are essential for page functionality and should load first .
  2. Other Scripts:For better performance, place non-critical scripts just before the closing </body> tag. - You can also include scripts in the head , but be mindful of page load times. Avoid placing scripts directly in markup (e.g., <input onclick="myFunction()">). Instead, use event handlers in your script bod
y

Remember, external files are preferred for JavaScript to keep your HTML clean and maintainable . (refer links)

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