My application has been growing for the last year or so and I have finally started to split out common components by extending existing ones. I've found this to be really helpful - increasing speed of development and maintenance. My problem is that I haven't grasped the concept of using custom parameters on my components and was hoping that someone could offer some assistance in the following example. Specifically I don't seem to be able to access the custom parameter (myCustomParam) inside the proxy declared in the initComponent function:

MyEmployeeGrid = Ext.extend(Ext.grid.GridPanel, {
     myCustomParam: "CompanyX",
     initComponent:function() {
        //Store Reader
        var myReader = new{
            root : 'objectsToConvertToRecords',
            idProperty: 'id',
            fields : [
                {name: 'id'},
                {name: 'employee', allowBlank:false},
                {name: 'department', allowBlank:false}
        //Store Proxy
        var dwrProxy = new{
                apiActionToHandlerMap : {
                read : {
                    dwrFunction : EmployeeService.readCompanyEmployees,
                    getDwrArgsFunction: function(request, recordDataArray, oldRecordDataArray) {
                        return [myCustomParam];
        //Setup Params for the grid
        Ext.apply(this, {
            store: new{
                 proxy: dwrProxy,
                reader: myReader,
                autoLoad : true,
                autoSave: true
            columns: [{header: "Employee", dataIndex: 'employee'},
                        {header: "Department", dataIndex: 'department'}]
        MyEmployeeGrid.superclass.initComponent.apply(this, arguments);
    } // eo function initComponent
    ,onRender:function() {
        MyEmployeeGrid.superclass.onRender.apply(this, arguments);
    } // eo function onRender
Ext.reg('myemployeegrid', MyEmployeeGrid);