This is an example of using a module pattern and closure together to build client-side CC/CEP extension modules.

cep-module-example.jsx

/**
 * @see https://github.com/Adobe-CEP/Samples/blob/master/XmpSamplePanel/js/xmp_bridge.js
 */

/*  
 * ADOBE SYSTEMS INCORPORATED
 * Copyright 2014 Adobe Systems Incorporated
 * All Rights Reserved.
 * 
 * NOTICE:  Adobe permits you to use, modify, and distribute this file in accordance with the 
 * terms of the Adobe license agreement accompanying it.  If you have received this file from a 
 * source other than Adobe, then your use, modification, or distribution of it requires the prior 
 * written permission of Adobe.
 */

/***************************************************************************************
 * -- XMPBridge ------------------------------------------------------------------------
 * 
 * The ExtendScript libraries are not directly accessible from the CEP HTML5 JavaScript 
 * engine. Interactions with the application DOM or other ExtendScript components need 
 * to be tunneled through the CSInterface. That component supports submitting
 * ExtendScript expressions to be evaluated within the application's scripting context 
 * and registering a callback function to capture the results. 
 * 
 * In order to provide a more convenient and high-level API the XMPBridge acts as a 
 * plain JavaScript proxy to the $.XMP utility that lives inside the ExtendScript 
 * environment.
 * 
 * As the communication happens in an asynchronous fashion you need to make sure that
 * you don't try to access XMP properties before the component is initialized properly
 * (e.g. the setup() method has completed). To address this the XMPBridge provides
 * an onInit() method, so you can register a callback that will be called once 
 * everything is ready to use.
 * 
 * sample usage:
 * 
 * XMPBridge.onInit(function(readyState) {
 * 
 *         if(!readyState.isError) {
 *         
 *             // now we're ready to go.
 *             XMPBridge.toNamespaceURI('NS_DC', function(namespaceUri) {
 *                 XMPBridge.read(namespaceUri, 'title');
 *             });
 *         
 *         } else {
 *             // error handling.
 *         }
 * 
 * });
 * 
 **************************************************************************************/
var MyPlugin = (function(exports) {
    
    var CS_INTERFACE = new CSInterface();
    var LOCAL_CACHE  = {};

// Private Methods -----------------------------------------------------------------------

    /**
     * handle multi-line string arguments.
     */
    function escape(arg) {
        return arg.replace(/\r\n?|\n/g, "\\n");
    }
    
    /**
     * helper function that constructs an ExtendScript expression dynamically from 
     * the arguments of its current invocation. All arguments are passed through
     * the escapeArgument() function which supports basic validation.
     * 
     * Expects the first argument to be a method/function name that is requested 
     * to be called. Any function argument will be registered as a callback.
     */
    function callExtendScript(method) {
        var args = [].splice.call(arguments,1);
        var callback = undefined;

        var params = [];
        for(var idx in args) {
            var arg = args[idx];
            if(typeof(arg) == 'function') {
                callback = arg;
            } else {
                params.push(escapeArgument(arg));
            }
        }
    
        var functionArgs = params.length ? '("' + params.join('","') + '")' : '()';
        var script = method + functionArgs;
        
        /*
         * evaluate against the ExtendScript context.
         */
        CS_INTERFACE.evalScript(script, callback);
    }
            
// Public Methods -----------------------------------------------------------------------
    
    /**
     * Initiates the setup process and accepts an event handler function that will be 
     * invoked once all components are ready to use. The callback is called with a single
     * argument that reports any error that occurred during the initialization.
     *  
     * e.g. sample readyState parameter:
     * 
     *  {
     *      isError: true,
     *      statusMessage "Application not supported."
     *  }
     */
    exports.onInit = (function() {
        
        var readyState = undefined;
        var callback   = undefined;
        
        // kick off setup phase regardless whether onInit() was called or not.
        // Note: this is a self-executing function closure.
        
        callExtendScript('theJsxMethod', CS_INTERFACE.getApplicationID(), function(result) {
            callback && callback({ 
                isError       : result != 'undefined' && result.trim() != '',
                statusMessage : result
            });
        });

        // The actual onInit() method. 
        // Will execute the initHandler immediately if setup() has already 
        // been completed or wait otherwise.
        
        return function(initHandler) {
            if (readyState) {
                initHandler(readyState);
            } 
            else {
                callback = initHandler;
            }
        };
        
    })();
    
    /**
     * @see $.MyClass#method()
     */
    exports.method = function() {
        callExtendScript('$.MyClass#method');    
    };
    
    return exports;
    
})(MyPlugin || {});