Bad value X for attribute “type” on element “script”: Subtype missing.

A MIME type (also called a media type) is composed of two parts: a type and a subtype, separated by a forward slash (/) with no whitespace. For example, text/javascript has text as the type and javascript as the subtype. When you specify a value like text or javascript alone — without the slash and the other component — the validator reports this error because the subtype is missing.

This error commonly occurs when authors confuse the MIME type format with a simple label, writing something like type="text" or type="javascript" instead of the full type="text/javascript". It can also happen due to a typo, such as accidentally omitting the slash or the subtype portion.

Why this matters

Browsers rely on the type attribute to determine how to process the contents of a <script> element. An invalid MIME type can cause browsers to misinterpret or skip the script entirely. While modern browsers default to JavaScript when no type is specified, providing a malformed MIME type is not the same as omitting it — it may lead to unpredictable behavior across different browsers and versions. Keeping your markup valid also ensures better tooling support and forward compatibility.

How to fix it

You have two main options:

1. Provide a complete, valid MIME type. For JavaScript, use text/javascript. For JSON data blocks, use application/json. For importmaps, use importmap.
2. Remove the type attribute entirely. Per the HTML specification, the default type for <script> is text/javascript, so omitting type is perfectly valid and is actually the recommended approach for standard JavaScript.

Examples

Incorrect: missing subtype

<!-- "text" alone is not a valid MIME type -->

<script type="text" src="app.js"></script>

<!-- "javascript" alone is not a valid MIME type -->

<script type="javascript" src="app.js"></script>

Correct: full MIME type specified

<script type="text/javascript" src="app.js"></script>

Correct: omitting the type attribute (recommended for JavaScript)

<script src="app.js"></script>

Since text/javascript is the default, omitting the attribute is the cleanest approach for standard JavaScript files.

Correct: using type for non-JavaScript purposes

The type attribute is still useful when embedding non-JavaScript content in a <script> element. In these cases, always use the full MIME type:

<script type="application/json" id="config">
  {"apiUrl": "https://example.com/api"}
</script>

<script type="importmap">
  { "imports": { "lodash": "/libs/lodash.js" } }
</script>

Common valid MIME types for <script>

Note that module and importmap are special values defined by the HTML specification and are not traditional MIME types, but they are valid values for the type attribute on <script> elements.

Learn more:

MDN Reference

MDN: Structure of a MIME type

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WHATWG Spec

HTML Spec: the script element

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MDN Reference

MDN: the script element

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