Answer by Jesse Dhillon for JSON object is null, even though feed is valid JSON

The api_response_format=jsonp:callback argument is supposed to be the name of a callback function defined in by your Javascript. So let's say I have a function called handleJson which is supposed to parse a JSON response, then you have to pass the argument jsonp:handleJson. Disqus will then pass you code wrapped in a call to handleJson.

What JSONP brings is the ability to get around the same-domain origin policy. Suppose that a URL <http://foo/json> responds with this JSON object:

{  id: 2,  first_name: 'John',  last_name: 'Doe',}

The only way you could use that object is if you are also on domain foo. But if you are not able to be on that domain, suppose that you are accessing an API that returns JSON format objects, then you ned a little help from that API provider.

Suppose that the url you request now becomes <http://foo/json?callback=handleJson> and the API provider responds with this:

handleJson({id: 2, first_name: 'John', last_name: 'Doe'})

Now, the browser is going to try to run that snippet of Javascript inside of the environment you've defined. So if you've defined a handleJson function, it's going to be called.

That's what JSONP is, a way to circumvent the same-domain origin policy and give you cross-site scripting with JSON objects.