The JSON data can directly be used as an object. If, for instance, your data looks like this:
you can write something like:
var Data := JSON.Parse(http.ResponseText);
which would write 'Bar' to the console.
If you want to use type information, you can write something like this:
JFooBar = class external
var Data := JFooBar(JSON.Parse(http.ResponseText));
The advantage of this approach is the fact that now code completion is aware of the 'Foo' member.
However, keep in mind that the type cast is unsafe. If the JSON data is not the class JFooBar it will result in an unpredictable behaviour (depending on read or write access).