Using serve returns incorrect mime types

[icedtoast]

When using the serve feature, esbuild returns the javascript files as "text/plain".
This causes an warning in Firefox:

The script from “http://localhost:8000/example.js” was loaded even though its MIME type (“text/plain”) is not a valid JavaScript MIME type.

More crucially if you are loading the entrypoint as WebWorker it will fail to load, with this error:

Loading Worker from “http://localhost:8000/exampleWorker.js” was blocked because of a disallowed MIME type (“text/plain”)

Is it possible to:
a) Change the serve feature to return the correct mime types (application/javascript for .js files)?
b) Allow customization of the mime types returned?

Also thanks for esbuild, it is amazing how much faster it makes javascript development.

[evanw]

That's weird. I get Content-Type: application/javascript and no warnings in Firefox when I try it locally. Can you provide detailed instructions for how to reproduce this?

[icedtoast]

Yes I thought it was strange too.

I am using Windows 10, if that helps

Steps to reproduce:

1. Create a javascript file with this content: console.log('hello');
2. Beside the javascript file add a folder called www
3. Open cmd.exe
4. cd to the folder containing your javascript file
5. Run npx esbuild example.js --servedir=www --outdir=www --bundle
6. Open localhost:8000 in firefox
7. Click the javascript file
8. Open Developer Tools, choose the network tab
9. Reload the page

Expected:
The javascript file is returned with a content type of application/javascript

Actual:
The javascript file is returned with a content type of text/plain.

You can also recreate with an html that refers to the javascript in the www folder, but I omitted that for brevity.

Screenshot of my developer tools:

[evanw]

How strange. Go's mime.TypeByExtension function seems to return different values when called on the string ".js". Still investigating.

Edit: Apparently this is a bug in Go: golang/go#32350. Dang. I'll just hard-code a list of mime types into esbuild then.

[jridgewell]

I'll just hard-code a list of mime types into esbuild then.

When you're doing this, can we update the mime-type to be text/javascript? Part of the standardization push for the .mjs extension was to return to text/javascript as the preferred mime type, and MDN has already updated to reflect this. It's also a "willful violation" as part of the HTML spec.

[jridgewell]

Ha, I see you've already done so: c8eb58f#diff-0c0053e1b4e1305cfa2461cf9f9512103c358ab97557cc123ced99ebc3934221R120