HTML async Attribute
Definition and Usage
async attribute is a boolean attribute.
When present, it specifies that the script will be executed asynchronously as soon as it is available.
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:
asyncis present: The script is executed asynchronously with the rest of the page (the script will be executed while the page continues the parsing)
asyncis not present and
deferis present: The script is executed when the page has finished parsing
- If neither
deferis present: The script is fetched and executed immediately, before the browser continues parsing the page
async attribute can be used on the following element:
A script that will be run asynchronously as soon as it is available:
The numbers in the table specify the first browser version that fully supports the attribute.