You promote data to code. JSON is usually a data format, like {result: 42}. If you wrap that in callback({result: 42}), that's executable javascript code. In

You promote data to code. JSON is usually a data format, like {result: 42}. If you wrap that in callback({result: 42}), that's executable javascript code. Including script tags on your pags via JS, like how the Delicious API / Flickr API / Google Translate & whatnot APIs, all rely on this. Check out http://developer.yahoo.com/common/json.html#callbackparam http://developer.yahoo.com/common/json.html#callbackparam