Google App Engine - Static files getting downloaded

Question

I've got a GAE application with a directory called static with two sub-directories css and js. Each of these directories have CSS and JavaScript files respectively. In my HTML code I've got references to these files such as:

<script src="/static/js/bootstrap-typeahead.js"></script>

And my app.yaml file looks like this:

application: ********
version: 1
runtime: python27
api_version: 1
threadsafe: yes

handlers:
- url: /static
  static_dir: static
- url: /favicon\.ico
  static_files: favicon.ico
  upload: favicon\.ico 
- url: /.*
  script: main.app

libraries:
- name: webapp2
  version: "2.5.2"
- name: jinja2
  version: latest

However, the CSS styles and JavaScript files aren't applied to the HTML code and when I view source and click on the links in the code, the CSS and JS files open up in a new tab and a download prompt pops up.

Q: Why are these files being downloaded instead of being linked with my HTML?

EDIT: I'm not sure if this is relevant but my GAE logs reveal that the request is returned with a 304 response:

INFO     2015-02-05 18:43:51,229 module.py:639] default: "GET /static/js/bootstrap-typeahead.js HTTP/1.1" 304 -

EDIT 2: Looking at my Google Chrome developer tools' network tab I came to know that the mime type for these files is application/x-js and application/x-css. Now, I'm certain that this is the cause of my problems but why is the mime type so when the docs clearly mention that,

By default, App Engine serves static files using a MIME type based on the filename extension. For example, a file with a name ending in .css will be served with a MIME type of text/css.

I tried modifying the mime type through app.yaml by explicitly specifying the mime types but it still doesn't change.

Answer 1

I had the same problem and I resolved to clean the staging bucket.

For do this, I open bucket section on my GCP console and you remove all file in the bucket with name staging.{projectname}.appspot.com