One of the most popular questions in ExtJs forums (stackoverflow) is how to extract data from non standard JSON and put it in store. First, I would like to suggest that you should avoid this trick. Try to speak with BackEnd developers and get appropriate JSON format for your application. However, if it is not possible, you can use the workarounds, which are described in this post.
“The name of a variable, function, or class, should answer all the big questions. It should tell you why it exists, what it does, and how it is used. If a name requires a comment, then the name does not reveal its intent.”
Practicing our professional life in writing clean code we forget to define clean interfaces between client and server sides.