JS：检查日期是否少于1小时？

有没有办法检查日期是否少于1小时？

Is there a way to check if a date is less than 1 hour ago?

这样的事情：

<script>
// old date
var olddate = new Date("February 9, 2012, 12:15");

// current date
var currentdate = new Date();

if (olddate >= currentdate - 1 hour) {
    alert("newer than 1 hour");
else {
    alert("older than 1 hour");
}
</script>

另外，不同的问题是 - 有没有办法增加约会时间？

Also, different question - is there a way to add hours to a date?

喜欢这样：

<script>
var olddate = new Date("February 9, 2012, 12:15") + 15 HOURS; // output: February 10, 2012, 3:15
</script>