async
Attribute for Script
Example
Check if the script executes asynchronously (as soon as it is available):
x Output result is:
Definition and Usage
The async
attribute sets or returns whether the script executes asynchronously (as soon as it is available).
This attribute reflects the async
attribute of the <script>
tag.
Note: The async
attribute is only applicable to external scripts (only when the src
attribute is used).
Note: There are several ways to execute external scripts:
If
async="async"
: The script executes asynchronously with the rest of the page (the script will be executed while the page continues to parse)If
async
is not used anddefer="defer"
: The script will be executed when the page has finished parsingIf neither
async
nordefer
is used: The script is fetched and executed immediately, before the browser continues parsing the page
Browser Support
All major browsers support the async
attribute.
Note: IE 9 and earlier versions, and Opera 12 and earlier versions do not support the async
attribute.
Syntax
Return the async
attribute:
Set the async
attribute:
Attribute Values
Value | Description |
---|---|
true/false | Specifies whether the script executes asynchronously (as soon as it is available). true - The script will be executed asynchronously as soon as it is available. false - The script will not be executed asynchronously (as soon as it is available). |
Technical Details
| Return Value: | Boolean, returns true if the script executes asynchronously (as soon as it is available), otherwise returns false. |
Related Articles
HTML Reference: HTML <script>
async Attribute