# An inline classic “script” element (i.e., a “script” element without a “src” attribute and with a “type” attribute that is either unspecified, empty, or a JavaScript MIME type) must not have an “async” attribute.

> Canonical HTML version: https://rocketvalidator.com/html-validation/an-inline-classic-script-element-i-e-a-script-element-without-a-src-attribute-and-with-a-type-attribute-that-is-either-unspecified-empty-or-a-javascript-mime-type-must-not-have-an-async-attribute
> Attribution: Rocket Validator (https://rocketvalidator.com)
> License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

The `async` attribute is invalid on an inline classic `<script>`, because there is no external file for the browser to fetch in the background.

`async` tells the browser to download a script while it keeps parsing the page, and to run it as soon as it arrives. The code of an inline script is already in the page, so the browser runs it right away and `async` changes nothing. A classic script is any `<script>` whose `type` is missing, empty or a JavaScript MIME type such as `text/javascript`.

Inline module scripts are the exception. On `<script type="module">`, `async` makes the module run as soon as it and its imports are ready, instead of waiting until the document has been parsed, so the validator accepts it there.

Templates and performance plugins that add `async` to every `<script>` cause most of these. Remove the attribute from the inline script, or move the code to an external file if it should load without blocking the parser.

## Invalid example

```html
<script async>
  console.log("Hello");
</script>
```

## Valid example

```html
<script>
  console.log("Hello");
</script>
```

To load the code without blocking the parser, put it in an external file and keep `async` on that `<script>`:

```html
<script src="app.js" async></script>
```