UML Class diagram from my code

I've build simple application in ExtJS and now I would like to create UML diagram showing classes and their relations.

Could You guys advice me how can I do that automatically? Maybe there is a tool to do that?

In Visual Studio we can create diagram and drag classes from solution to it and it is automatically showing methods and properties of those classes. But this doesn't work with JavaScript and ExtJS.

KinectRecorderClassDiagram.png

Can I do something similar with JS (ExtJS) code in my application?