js根据年月获取这月的开始日期和结束日期

if(vars.ny!=null&&vars.ny!=''){
            var nyYear=vars.ny.slice(0,4);
            var nyMonth=vars.ny.slice(4,vars.ny.length);
            var firstDay = new Date(nyYear,nyMonth-1);
            var lastDay = new Date(new Date(nyYear,nyMonth).valueOf()-60*60*1000*24);
            function datasFormat(d){
                var datetime=d.getFullYear() + '-' + (d.getMonth() + 1) + '-' + d.getDate();
                return datetime;
            }

            vars.sjksrq=datasFormat(firstDay)
            vars.sjjsrq=datasFormat(lastDay)
            fzscdatas[15]=vars.sjksrq;
            fzscdatas[16]=vars.sjjsrq;
        }

这里的vars.ny 字段如：201603
输出结果为：2016-03-01  2016-03-31