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HTML5 <script> defer Attribute

HTML5 script Tag Reference HTML5 <script> tag

Example

A script that will not run until after the page has loaded:

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

Try it yourself »

Browser Support

Internet Explorer Firefox Opera Google Chrome Safari

The defer attribute is supported in all major browsers.

Definition and Usage

The defer attribute is a boolean attribute.

When present, it specifies that the script is executed when the page has finished parsing.

Note: The defer attribute is only for external scripts (should only be used if the src attribute is present).

Note: There are several ways an external script can be executed:

  • If async="async": The script is executed asynchronously with the rest of the page (the script will be executed while the page continues the parsing)
  • If async is not present and defer="defer": The script is executed when the page has finished parsing
  • If neither async or defer is present: The script is fetched and executed immediately, before the browser continues parsing the page

Differences Between HTML 4.01 and HTML5

None.

Syntax

<script defer="defer">

Note: The defer attribute is a boolean attribute, and can be set in the following ways:

  • <script defer>
  • <script defer="defer">
  • <script defer="">
HTML5 script Tag Reference HTML5 <script> tag
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