text/css and text/javascript — Serving Web Assets Correctly

Serving CSS and JavaScript

Modern browsers are strict about MIME types for stylesheets and scripts. Serving them with the wrong type can cause silent failures.

text/css

Content-Type: text/css; charset=utf-8

Browsers refuse to apply a stylesheet if the response Content-Type is not text/css. This is a security measure called MIME type checking (enforced when X-Content-Type-Options: nosniff is set).

text/javascript

Content-Type: text/javascript; charset=utf-8

RFC 9239 (2022) established text/javascript as the single official type for JavaScript. The following legacy types still work but are deprecated:

Legacy Type	Status
application/javascript	Deprecated (RFC 9239)
application/x-javascript	Non-standard
text/ecmascript	Deprecated
application/ecmascript	Deprecated

Module Scripts

ES modules loaded with <script type="module"> still use text/javascript as their Content-Type. The type="module" attribute is an HTML attribute, not a MIME type.

Common Server Misconfigurations

Problem	Symptom
CSS served as text/plain	Styles not applied
JS served as application/octet-stream	Script blocked
Missing charset	Encoding issues with non-ASCII

Nginx Configuration

types {
    text/css                css;
    text/javascript         js mjs;
}

TypeScript Files

TypeScript (.ts) files are transpiled to JavaScript before serving. They should never be served directly to browsers. For development servers, application/typescript is sometimes used but has no official IANA registration.