EXTJS grid 表格 javascript

function fn(){
    
//顶部工具栏
    var tbar=[{
           id:'btnAdd',
            text:'新增',
            tooltip:'新增',
           iconCls:'ico_add',
           handler: showAddPanel
        }, '-', {
            text:'查询',
           // tooltip:'查询',
           iconCls:'ico_search'
        }, '-', {
            text:'批量删除',
            //tooltip:'删除',
            iconCls:'ico_del',
            //handler:showDelDialog
        }
        ];
    //底部工具栏
var bbar=new Ext.PagingToolbar({
    emptyMsg: '没有记录',    
    beforePageText :'第',   
   afterPageText :'页,共  {0}  页',   
    displayMsg: '显示第 {0} 条到 {1} 条记录，一共 {2} 条',
     store:store
  });
  //json地址
   var url="json_grid/Handler.ashx";
   //
  var fields=[{name:"hca_art_id"},{name:"hca_art_title"},{name:"hca_art_author"},{name:"hca_art_ComputerName"},{name:"hca_art_date"}];
//多选择按钮
  var sm = new Ext.grid.CheckboxSelectionModel();  
  //序号
  var nm = new Ext.grid.RowNumberer();
//表格列选项
 var cm=new Ext.grid.ColumnModel(
                                [nm,sm,
                                {header:"ID",dataIndex:"hca_art_id"},{header:"标题",dataIndex:"hca_art_title"},{header:"作者",dataIndex:"hca_art_author"},{header:"计算机名",dataIndex:"hca_art_ComputerName"},{header:"日期",dataIndex:"hca_art_date"}
                                      ] );
//store 设置
     var store=new Ext.data.Store({
                 proxy:new Ext.data.HttpProxy({url:url}),
                 reader:new Ext.data.JsonReader({totalProperty:"totalCounts",root:"data",fields:fields})
                 });
 store.load({params:{start:0,limit:40}}); 

//grid
     var grid=new Ext.grid.GridPanel({
                                     el:"ext_grid",
                                     height:300,
                                     store:store,
                                     cm:cm,
                                     sm:sm,
                                     title:"测试",
                                     tbar:tbar,
                                      bbar: bbar
                                       });
 grid.render();
  }
Ext.onReady(fn);