How to mark script element as Asynchronous
Description
async which applies only to external scripts
changes the way the script is processed.
It signals the browser to begin downloading the file immediately.
async scripts are not guaranteed to execute in the order in which they are specified.
Example
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript" async src="example1.js"></script>
<script type="text/javascript" async src="example2.js"></script>
</head>
<body>
<!-- content here -->
</body>
</html>
Note
In this code, the second script file might execute before the first.
For XHTML documents, specify the async attribute as async="async".