ext editgrid 客户端 设置新值

下面是一个ext页面，不与服务器交互，只是客户端的行为。
我想点击第一行的数据后，
输入新的值，并可以
1、显示在页面上
2、保存到store<html>
<head>
<script type="text/javascript" src="extjs/ext-lang-zh_CN.js"></script>
<script type="text/javascript" src="extjs/adapter/ext/ext-base.js"></script>
<script type="text/javascript" src="extjs/ext-all.js"></script>
<link rel="stylesheet" type="text/css"
href="extjs/resources/css/ext-all.css" />
<title></title>
</head>
<script>back=[{"point":"","arrive_time":"","range":"111"},{"point":"2","arrive_time":"22","range":"222"}];Ext.onReady(function(){
var already_cm=new Ext.grid.ColumnModel([
      new Ext.grid.RowNumberer({header:'序号',width:30}),
      {header:'到达时间',hideable:false,editor:new Ext.form.TimeField()},
      {header:'误差范围',hideable:false,editor:new Ext.form.TextField({maxLength : 5})}
      ]);
           
var already_store=new Ext.data.JsonStore({data:back,fields:['pointid','arrive_time','range']});var already_grid = new Ext.grid.EditorGridPanel({
        renderTo: 'line_base_modify',
        store: already_store,
        id:'a',
        mode:'local',
        cm: already_cm,
        height:300,
        clicksToEdit : 1
    });already_grid.on("afteredit",afterEdit,this);

});
function afterEdit(obj){
var r=obj.record;
alert(r.data['range']);
alert(99);
//Ext.getCmp('a').getStore();
//Ext.getCmp('a').getStore().reload();
alert(88);
}</script>
<body>
<div id='line_base_modify'></div>
</body>
</html>