If you need this alot, you could just add it as a plugin:

$.postJSON = fuction(url, data, callback) {
	$.post(url, data, callback, "json");
};

This saves about 2 characters per use, not really that very handy...

Any example of it?

I've used this script quite successfully: http://www.thomasfrank.se/json_stringify_revisited.html

I have an app that stores data in a JSON object as a user is doing things. In order to get that JS object to the server to do something useful with it, it has to be converted to a string first. "JSONstring.make(myobject)" does just that. It's like Serialize, but for JSON.

I agree it would be useful to have build it, but I don't mind including an external script to do it.