Getting the default file extension for a content-type in JavaScript?

Question

If I have a content-type, how can I get its default file extension?

For example, given one of these content-types, I should get the following file extensions:

+------------------------+----------------+
|      Content-Type      | File Extension |
+------------------------+----------------+
| text/plain             | .txt           |
| application/javascript | .js            |
| application/gzip       | .gz            |
+------------------------+----------------+

If there is no way to get these extensions automatically in JavaScript, my next solution would be to create a simple relationship between content-type and file extension in a JavaScript array. Therefore, I would accept an answer which has a simple table/database of the most common content-type and file extensions.

Answer 1

For Node applications, there is a more up-to-date answer now, which is to use the mime-types NPM package, e.g.:

var mime = require('mime-types'),
    fileExtension = mime.extension('text/plain');