HTML Guide for async
The async attribute is boolean: the presence of a boolean attribute on an element represents the true value, and the absence of the attribute represents the false value. As a boolean attribute, it does not need to be passed any value such as true or 1 to activate the async property.
For classic scripts, if the async attribute is present, then the classic script will be fetched in parallel to parsing and evaluated as soon as it is available.
For module scripts, if the async attribute is present then the scripts and all their dependencies will be executed in the defer queue, therefore they will get fetched in parallel to parsing and evaluated as soon as they are available.
<script async src="app.js"></script>
<script async type="module">
/* JavaScript module code here */
</script>There is an illegal double quote character (") at the end of the src attribute value in your <script> tag, which causes the attribute to be invalid.
Attribute values must not include unescaped or stray quote characters (" or ') inside them, as this breaks attribute parsing and results in invalid HTML. The src attribute for a <script> tag should contain a properly encoded URL without any stray quotes or illegal characters. In your case, a double quote has accidentally been included before the closing quote of the attribute.
Correct usage for a <script> tag with the async attribute is:
<script src="https://example.com/js/jquery-3.6.0.min.js?ver=6.8.2" async></script>Incorrect example with the error (shows the issue):
<script src="https://example.com/js/jquery-3.6.0.min.js?ver=6.8.2" async""></script>Make sure there are no stray characters in your attribute values and that boolean attributes like async do not have values—it should simply be present, as in async, not async"" or async="async".
If you need a full, minimal HTML document to validate, use:
<!DOCTYPE html>
<html lang="en">
<head>
<title>Valid Script Tag Example</title>
</head>
<body>
<script src="https://example.com/js/jquery-3.6.0.min.js?ver=6.8.2" async></script>
</body>
</html>Double-check your HTML source code to ensure there are no accidental typos or misplaced quote marks in your tag attributes.
The async and defer boolean attributes of the <script> element control how an external script should be executed once it has been downloaded. The async attribute makes sense when an external script (defined with the src attribute) is loaded, or when defining a script of type module:
<script async src="app.js"></script>
<script async type="module">
/* JavaScript module code here */
</script>