JavaScript如何获得昨天明天等日期

<script type="text/javascript">
function GetDateStr(AddDayCount) {
    var dd = new Date();
    dd.setDate(dd.getDate()+AddDayCount);//获取AddDayCount天后的日期
    var y = dd.getFullYear();
    var m = dd.getMonth()+1;//获取当前月份的日期
    var d = dd.getDate();
    return y+"-"+m+"-"+d;
}
document.write("前天："+GetDateStr(-2));
document.write("<br />昨天："+GetDateStr(-1));
document.write("<br />今天："+GetDateStr(0));
document.write("<br />明天："+GetDateStr(1));
document.write("<br />后天："+GetDateStr(2));
document.write("<br />大后天："+GetDateStr(3));
</script>