Ext JS 4 reorganized the API packages names and as a consequence, some classes has a new class name now. The Ext JS 3 class names are still valid in Ext JS 4, but when we are migrating an app from Ext JS 3 to Ext JS 4, it is recommended to change the class name as well.
That being said, I created a simple application where you can quickly search for a Ext JS 3 class name and find its correspondent Ext JS 4 class name. This application contains only the classes which name have changed.
I hope this can help someone.
And I am open for suggestions to improve this app.