(This book is the second edition of experiencing ext JS, which covers the new features of ext 3x and is a supplement to the previous edition. This book introduces ext events, core components, forms, forms and other controls, tree structure, drag and drop, pop-up windows, layout, data storage and transmission, and practical tools in detail. Each knowledge point has corresponding and strong operability. Two powerful examples are added, including how to optimize the application based on ext, improve the loading speed, how to create user extension components and common third-party extensions.This book is suitable for all web developers.)