Javascript MIME Type not Set Properly

Question

I'm building some web apps with Python/Tornado.

Some of my (HTML) pages have:

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

When I load the page in FireFox, I get the warning:

"The script from “http://localhost:8086/static/some_script.js” was loaded even though its MIME type (“text/plain”) is not a valid JavaScript MIME type."

Why does the browser think the MIME type is "text/plain" instead of "text/javascript"? Where is it getting that idea from....?

I also load:

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

and

<script src="//cdnjs.cloudflare.com/ajax/libs/socket.io/0.9.16/socket.io.min.js" type="text/javascript"></script>

for which I don't get the same warning.....

Answer 1

Mime type is something the server send as header detail and it's usually based on file extension, but it can be enforced as needed.

If you run your Web page/application locally, you need to spin a webserver for that folder, as opening the .html file directly will not work, or better, requested files will not be served with the correct mime type.

Use a webserver, and you'll never see this error again.

Answer 2

I had the same problem but with ExpressJS application. For me, path to the concerned static file was not correct. So exressjs(web server) defaulted to text/html mime type.

so check if "/static/some_script.js" path is correctly directing to the static file (some_script.js)