关于js接收后台时间戳转换成时间问题

后台回传数据
work[name:"...",id:"...",checkdata:"2017-7-28".....]
经过toJSONString后checkdata变成了4141415765415(时间戳)

List<Work> works=this.workBiz.findWork(classid, semester, checkDate,page,rows);
int total=workBiz.findworknum(classid,null,null,null);
Map<String,Object> map=new HashMap<String,Object>();
map.put("rows", works);
map.put("total", total);
jsonStr=JSON.toJSONString(map);

datagrid=$("#show_find_checkwork").datagrid({
url:"/Examination2.0/work_findWorkresult.action",//加载的URL
pagination:true,//显示分页
pageSize:10,//分页大小
pageList:[5,10,15,20],//每页的个数
fit:true,//自动补全
toolbar : '#find_table_slelct',
fitColumns:true,
queryParams : {
examineeclassid:classname,
chackdate:checkDate,
semester:semester,
editionid:editionid,
subjectid:subjectid,
chapterid:chapterid,
},
iconCls:"icon-save",//图标
columns:[[      //每个列具体内容
{
field:'wid',
title:'编号',
width:50,
},
{field:'wname',title:'作业名',align :'center',width:100},
{field:'checkdate',title:'检查时间',align : 'center',width:100,
formatter : function(value, row, index) {
return change(row.checkdate)
}},
{field:'description',title:'作业描述',align : 'center',width:200},
{field:'remark',title:'备注',align : 'center',width:100} ,
{field:'result',title:'操作',align : 'center',width:100,
formatter : function(value, row, index) {
if(row.result!=null&&row.result!=""&&row.result!=undefined){
return '<a href=\"changefindwork.jsp?wid='+row.wid+'">查看</a>';
}else{
return '<label>未检查</label>';
}

}}
]]
})

function change(data) {
var birthday = new Date(data);
var time=birthday.toLocaleString()
//"2017/7/28 上午 12:12:12"
time=time.replace(/上午(\w|:)*/,"");
//"2017/7/28 "
//time=time.replace(/\s$/,"");
return time;
}