ExtJS Naming Convention:

Ext JS is a JavaScript framework. Therefore, you should follow most of the JavaScript naming conventions.

Sencha suggests following naming conventions for Ext JS application:

Convention for Description
Class Class name should be in CamelCase
Class name should contain alphanumeric characters. Numbers are permitted if it belongs to a technical term.
Do not use underscores, hyphens, or any other non-alphanumeric characters.
Class name should be with at least one unique namespace separated by dot (.).
Classes that are not distributed by Sencha should never use Ext as the top-level namespace.
The top-level namespaces and the actual class names should be in CamelCase, everything else should be in lower-case.
Source File The names of the classes map directly to the file paths in which they are stored. As a result, there must only be one class per file. Ext.util.Observable is stored in path/to/src/Ext/util/Observable.js MyTopLevelNamespace.util.JsonToXml is tored in path/to/src/MyTopLevelNamespace/util/ JsonToXml.js
Methods Method should always be in camelCase.
Variables Variable should always be in camelCase.
Constant variable should be in upper-case
Private variable should start with underscore ‘_’
Properties Properties should always be in camelCase. Static properties should bein upper-case.

Also, visit javascript.crockford.com for JavaScript coding conventions used in JSLint.