The source code

    Ext.app.App = function(cfg){
        Ext.apply(this, cfg);
        this.addEvents({
            'ready' : true,
            'beforeunload' : true
        });

        Ext.onReady(this.initApp, this);
    };

    Ext.extend(Ext.app.App, Ext.util.Observable, {
        isReady: false,
        startMenu: null,
        modules: null,

        getStartConfig : function(){

        },

        initApp : function(){
        	this.startConfig = this.startConfig || this.getStartConfig();

            this.desktop = new Ext.Desktop(this);

    		this.launcher = this.desktop.taskbar.startMenu;

    		this.modules = this.getModules();
            if(this.modules){
                this.initModules(this.modules);
            }

            this.init();

            Ext.EventManager.on(window, 'beforeunload', this.onUnload, this);
    		this.fireEvent('ready', this);
            this.isReady = true;
        },

        getModules : Ext.emptyFn,
        init : Ext.emptyFn,

        initModules : function(ms){
    		for(var i = 0, len = ms.length; i < len; i++){
                var m = ms[i];
                this.launcher.add(m.launcher);
                m.app = this;
            }
        },

        getModule : function(name){
        	var ms = this.modules;
        	for(var i = 0, len = ms.length; i < len; i++){
        		if(ms[i].id == name || ms[i].appType == name){
        			return ms[i];
    			}
            }
            return '';
        },

        onReady : function(fn, scope){
            if(!this.isReady){
                this.on('ready', fn, scope);
            }else{
                fn.call(scope, this);
            }
        },

        getDesktop : function(){
            return this.desktop;
        },

        onUnload : function(e){
            if(this.fireEvent('beforeunload', this) === false){
                e.stopEvent();
            }
        }
    });