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 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 async attribute can be used on the following element:

Example

Browser Support

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