Ext4 grid显示有关问题

Ext.onReady(function() {          Ext.define('simpsonsStore',{            extend:'Ext.data.Store',            fields:['name', 'email', 'phone'],            data:{'items':[                {"name":"Lisa", "email":"lisa@simpsons.com", "phone":"555-111-1224"},                {"name":"Bart", "email":"bart@simpsons.com", "phone":"555--222-1234"},                {"name":"Homer", "email":"home@simpsons.com", "phone":"555-222-1244"},                {"name":"Marge", "email":"marge@simpsons.com", "phone":"555-222-1254"}            ]},            proxy: {                type: 'memory',                reader: {                    type: 'json',                    root: 'items'                }            }        });                       Ext.create('Ext.grid.Panel', {              title: 'Simpsons',              store: new simpsonsStore,              columns: [                  {header: 'Name',  dataIndex: 'name'},                  {header: 'Email', dataIndex: 'email', flex:1},                  {header: 'Phone', dataIndex: 'phone'}              ],              height: 200,              width: 400,              renderTo: Ext.getBody()          });    })