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HTML defer Attribute


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 is present: 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 is present: 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

Applies to

The defer attribute can be used on the following element:

Element Attribute
<script> defer

Example

Example

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

<script src="demo_defer.js" defer></script>
Try it Yourself »

Browser Support

The numbers in the table specify the first browser version that fully supports the attribute.

Attribute
defer Yes 10.0 3.6 Yes 15.0