一个小问题

我按照网站上面的文章来写的例子，。

Ext.onReady(function() {
	var myData = [
		['Apple',29.89,0.24,0.81,'9/1 12:00am'],
		['Ext',83.81,0.28,0.34,'9/12 12:00am'],
		['Google',71.72,0.02,0.03,'10/1 12:00am'],
		['Microsoft',52.55,0.01,0.02,'7/4 12:00am'],
		['Yahoo!',29.01,0.42,1.47,'5/22 12:00am']
	];

	var ds = new Ext.data.Store({
		proxy: new Ext.data.MemoryProxy(myData),
		reader: new Ext.data.ArrayReader({id: 0}, [
			{name: 'company'},
			{name: 'price', type: 'float'},
			{name: 'change', type: 'float'},
			{name: 'pctChange', type: 'float'},
			{name: 'lastChange', type: 'date', dateFormat: 'n/j h:ia'}
	])
	});
	ds.load();

	var colModel = new Ext.grid.ColumnModel([
		{header: "Company", width: 120, sortable: true, dataIndex: 'company'},
		{header: "Price", width: 90, sortable: true, dataIndex: 'price'},
		{header: "Change", width: 90, sortable: true, dataIndex: 'change'},
		{header: "% Change", width: 90, sortable: true, dataIndex: 'pctChange'},
		{header: "Last Updated", width: 120, sortable: true,
		renderer: Ext.util.Format.dateRenderer('m/d/Y'), dataIndex: 'lastChange'}
	]);

	var grid = new Ext.grid.GridPanel({el: 'grid-example', ds: ds, cm: colModel});
		grid.render();
		grid.getSelectionModel().selectFirstRow();
	});