自己写的其实还是不懂，
再看看别人写的吧
Extjs4 源码分析系列一 类的创建过程
https://www.cnblogs.com/creazyguagua/p/4302864.html
http://www.cnblogs.com/creazyguagua/p/4667768.html

ExtJs4 makeCtor初步理解！
http://blog.csdn.net/wjy397/article/details/47321255

extjs底层源码实现继承分析
http://www.cnblogs.com/ouzilin/p/5164302.html

Ext.define('MyApp.view.system.permission.Permission', {

    extend : 'Ext.panel.Panel',

    xtype : 'sys-permission',

    requires: [

        'MyApp.ux.Util',

        'MyApp.model.SysRole'

    ],

    viewModel: {

        stores: {

            roleStore : ZUtil.createStore('SysRole', 'SysRole/read'),

            treeStore: ZUtil.createTreeStore('SysMainMenu/getMenuTree', {autoLoad :false})

        }

    },

    controller: {

        type: 'sys-permission'

    },

    title : '权限管理',

    layout : 'border',

    items : [ {

        region : 'west',

        xtype : 'grid',

        width : 200,

        title : '角色列表',

        reference: 'grid',

        split: true,

        bind : {

            store : '{roleStore}'

        },

        selModel : {

            selType : 'rowmodel'

        },

        columns : [ {

            text : 'ID',

            dataIndex : 'id',

            hidden: true

        }, {

            text : '角色名称',

            dataIndex : 'name',

            flex: 1

        } ],

        listeners : {

            //activate : 'onRoleActivate',

            itemclick : 'onRoleClick'

        }

    }, {

        region : 'center',

        xtype : 'treepanel',

        title : '权限列表',

        rootVisible: false,

        reference: 'tree',

        bind : {

            store : '{treeStore}'

        },

        bbar: {

            items: [{

                text: '保存',

                iconCls: 'Disk',

                handler: 'onPermissionSave'

            }]

        }

    } ]

});

define: function (className, data, createdFn) {

            //<debug>

            Ext.classSystemMonitor && Ext.classSystemMonitor(className, 'ClassManager#define', arguments);

            //</debug>

            if (data.override) {

                Manager.classState[className] = 20;

                return Manager.createOverride.apply(Manager, arguments);

            }

            Manager.classState[className] = 10;

            return Manager.create.apply(Manager, arguments);

        },

/**

         * Defines a class.

         * @deprecated Use {@link Ext#define} instead, as that also supports creating overrides.

         * @private

         */

        create: function(className, data, createdFn) {

            //<debug>

            if (className != null && typeof className !== 'string') {

                throw new Error("[Ext.define] Invalid class name '" + className + "' specified, must be a non-empty string");

            }

            //</debug>

            var ctor = makeCtor(className);

            if (typeof data === 'function') {

                data = data(ctor);

            }

            //<debug>

            if (className) {

                if (Manager.classes[className]) {

                    Ext.log.warn("[Ext.define] Duplicate class name '" + className + "' specified, must be a non-empty string");

                }

                ctor.name = className;

            }

            //</debug>

            data.$className = className;

            return new Class(ctor, data, function() {
　　　　　　　　　　// 下面的createFn的处理估计是为了把类定义是的配置对象保存起来吧，
　　　　　　　　　　// 因为define一个自定义的类，就是为了设置上个性化的配置，从而Ext.create的时候直接得到个性化的实例

                var postprocessorStack = data.postprocessors || Manager.defaultPostprocessors,

                    registeredPostprocessors = Manager.postprocessors,

                    postprocessors = [],

                    postprocessor, i, ln, j, subLn, postprocessorProperties, postprocessorProperty;

                delete data.postprocessors;

                for (i = 0,ln = postprocessorStack.length; i < ln; i++) {

                    postprocessor = postprocessorStack[i];

                    if (typeof postprocessor === 'string') {

                        postprocessor = registeredPostprocessors[postprocessor];

                        postprocessorProperties = postprocessor.properties;

                        if (postprocessorProperties === true) {

                            postprocessors.push(postprocessor.fn);

                        }

                        else if (postprocessorProperties) {

                            for (j = 0,subLn = postprocessorProperties.length; j < subLn; j++) {

                                postprocessorProperty = postprocessorProperties[j];

                                if (data.hasOwnProperty(postprocessorProperty)) {

                                    postprocessors.push(postprocessor.fn);

                                    break;

                                }

                            }

                        }

                    }

                    else {

                        postprocessors.push(postprocessor);

                    }

                }

                data.postprocessors = postprocessors;

                data.createdFn = createdFn;

                Manager.processCreate(className, this, data);

            });

        },

/**

     * @method constructor

     * Create a new anonymous class.

     *

     * @param {Object} data An object represent the properties of this class

     * @param {Function} onCreated Optional, the callback function to be executed when this class is fully created.

     * Note that the creation process can be asynchronous depending on the pre-processors used.

     *

     * @return {Ext.Base} The newly created class

     */

    Ext.Class = ExtClass = function(Class, data, onCreated) {

        if (typeof Class != 'function') {

            onCreated = data;

            data = Class;

            Class = null;

        }

        if (!data) {

            data = {};

        }

        Class = ExtClass.create(Class, data);

        ExtClass.process(Class, data, onCreated);

        return Class;

    };

/**

         * @private

         */

        create: function (Class, data) {

            var i = baseStaticMembers.length,

                name;

            if (!Class) {

                Class = makeCtor(

                    //<debug>

                    data.$className

                    //</debug>

                );

            }

            while (i--) {

                name = baseStaticMembers[i];

                Class[name] = Base[name];

            }

            return Class;

        },

// Creates a constructor that has nothing extra in its scope chain.

    function makeCtor (className) {

        function constructor () {

            // Opera has some problems returning from a constructor when Dragonfly isn't running. The || null seems to

            // be sufficient to stop it misbehaving. Known to be required against 10.53, 11.51 and 11.61.

            return this.constructor.apply(this, arguments) || null;

        }

        //<debug>

        if (className) {

            constructor.name = className;

        }

        //</debug>

        return constructor;

    }