How to support both json and jsonp responses in node.js + Express?

I'm have a REST API service, written on Node.js + Express, which currently support responses in JSON format.

Now, I need to add support for JSONP responses too, so everyone may get it by adding alt=JSONP to the request string.

So, my question is, which is the best way to do so?

Possible, there is an pattern, or living example?

Thanks!

json
node.js
rest
express
jsonp

The officially supported method is as follows --

First, set your JSONP callback parameter name:

app.set('jsonp callback name', 'callback');

Then, change all instances of res.json or res.send to res.jsonp. For example, res.jsonp(500, { error: 'message' })

If the callback parameter is supplied in a request, the response will be wrapped as JSONP using the supplied function name, but if it isn't, it'll just return JSON.

Afterwards, this returns JSONP: GET /myapi/v1/users?callback=responseCallback

This does not: GET /myapi/v1/users

Reference http://expressjs.com/4x/api.html#res.jsonp