Add .mjs to known JS MIME types

[Bradley Meck]

I was told to make a ticket here per the mailing list thread: ​http://mailman.nginx.org/pipermail/nginx-devel/2021-July/014176.html

.mjs is supported by Node.js, is in JS specification examples ( E.G. ​https://tc39.es/ecma262/#sec-hostresolveimportedmodule ), and WHATWG specification examples ( ​https://html.spec.whatwg.org/multipage/webappapis.html#integration-with-the-javascript-module-system ), and has an upcoming MIME update per IETF ( ​https://datatracker.ietf.org/doc/draft-ietf-dispatch-javascript-mjs/ ). It is also supported by various existing MIME databases and serves properly on various hosts like Github Pages without custom configuration.

[Maxim Dounin]

For the record, a few relevant links:

• Originally introduced and seems to be mainly used by Node.js to ​distinguish ECMAScript modules from CommonJS modules.
• Introduced in examples in WHATWG specification with the questionable claim that ​extensions don't matter.
• Not currently recommended by ​Mozilla Dev Docs unless the environment is known to support .mjs.
• Not in ​Apache mime.types (​bug 61383).
• In ​Python.
• In ​mime-db as used by Github Pages.
• Presented as an alternative extension for JavaScript types in ​a draft to update RFC 4329.

Overall seems to be only important in Node.js ecosystem, where the .js extension means project-default module type, while .mjs and .cjs mean ECMAScript and CommonJS modules, respectively. While it might be usable to distinguish modules from scripts in the web, there is no clear difference. It is also not clear if we need to provide support in the default mime.types.

[Maxim Dounin]

See also:

​https://mailman.nginx.org/pipermail/nginx-devel/2022-May/7PN54GRH2S4ESBBTUTGZDXEKPEZGCWOJ.html

[Mathias Bynens]

This is now defined by RFC 9239: ​https://www.rfc-editor.org/rfc/rfc9239 Two changes are needed in the nginx codebase:

1. First, the recommended MIME type for JavaScript is now text/javascript.
2. Second, the .mjs extension is now explicitly registered.

The patch Maxim already pointed to addresses both points. What can we do to help get it reviewed + merged?