How do I trigger a function when the time reaches a specific time

I want to trigger a javascript function when the time reaches, say, 3:00 PM.

The time will 开发者_运维百科be assigned dynamically. So is there any javascript function to achieve that??

You just need to calculate the difference between the current time and the target time and use setTimeout() with that value.

For example, depending on how your target browsers parse dates, you could do the following:

function alert3pm() {
  alert("It's 3PM!");
}
var timeAt3pm = new Date("1/31/2011 03:00:00 PM").getTime()
  , timeNow = new Date().getTime()
  , offsetMillis = timeAt3pm - timeNow;
setTimeout(alert3pm, offsetMillis);

Or rather, instead of parsing a date (since that's really inconsistent between browsers) you could do something like this:

function getTimeAtHour(hour) {
  var t = new Date();
  t.setHours(hour);
  t.setMinutes(0);
  t.setSeconds(0);
  t.setMilliseconds(0);
  return t;
}