HTML async Attribute
Definition and Usage
The
async
attribute is a boolean attribute.
When present, it specifies that the script will be executed asynchronously as soon as it is available.
Note: The
async
attribute is only for external scripts (and 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 anddefer
is present: The script is executed when the page has finished parsing - If neither
async
ordefer
is present: The script is fetched and executed immediately, before the browser continues parsing the page
Applies to
The
async
attribute can be used on the following element:
Elements | Attribute |
---|---|
<script> | async |
Example
Script Example
A script that will be run asynchronously as soon as it is available:
<script src="demo_async.js" async></script>
Try it Yourself »
Browser Support
The numbers in the table specify the first browser version that fully supports the attribute.
Attribute | |||||
---|---|---|---|---|---|
async | Yes | 10.0 | 3.6 | Yes | Yes |