Adding JS Modules support to python's simpleHTTPServer

Recently I’ve been playing a lot with JavaScript modules but every once in a while I start a web server using python SimpleHTTPServer from the command line while forgetting it doesn’t know how to serve .mjs files. I keep running into the following error:

Failed to load module script: The server responded with a non-JavaScript MIME type of "application/octet-stream".
Strict MIME type checking is enforced for module scripts per HTML spec.

This error makes perfect sense since python doesn’t know what the .mjs extension is and it uses the default mime type of application/octet-stream.

The only problem is that JavaScript modules MUST return a proper JavaScript MIME [0] type in order for the user agent to execute it as JavaScript.

There are multiple ways you can fix this problem but I decided to make python aware of the new extension by adding a new file called mime.types at /usr/local/etc/mime.types [1] with the following content:

# Add proper mime type for mjs files.
application/javascript                          js mjs

Now when running python -m SimpleHTTPServer 8000 or python3 -m http.server 8000 JavaScript .mjs files just work.





javascript python