How to round to nearest hour using JavaScript Date Object

Question

I am working on a project that requires a time in the future to be set using the Date object.

For example:

futureTime = new Date();
futureTime.setHours(futureTime.getHours()+2);

My questions is; once the future date is set, how can I round to the closest full hour and then set the futureTime var with it?

For example:

Given 8:55 => var futureTime = 9:00
Given 16:23 => var futureTime = 16:00

Any help would be appreciated!

Answer 1

Round the minutes and then clear the minutes:

var date = new Date(2011,1,1,4,55); // 4:55
roundMinutes(date); // 5:00

function roundMinutes(date) {

    date.setHours(date.getHours() + Math.round(date.getMinutes()/60));
    date.setMinutes(0, 0, 0); // Resets also seconds and milliseconds

    return date;
}

Answer 2

The other answers ignore seconds and milliseconds components of the date.

The accepted answer has been updated to handle milliseconds, but it still does not handle daylight savings time properly.

I would do something like this:

function roundToHour(date) {
  p = 60 * 60 * 1000; // milliseconds in an hour
  return new Date(Math.round(date.getTime() / p ) * p);
}

var date = new Date(2011,1,1,4,55); // 4:55
roundToHour(date); // 5:00

date = new Date(2011,1,1,4,25); // 4:25
roundToHour(date); // 4:00

Answer 3

A slightly simpler way :

var d = new Date();
d.setMinutes (d.getMinutes() + 30);
d.setMinutes (0);

Answer 4

Another solution, which is no where near as graceful as IAbstractDownvoteFactory's

var d = new Date();
if(d.getMinutes() >= 30) {
   d.setHours(d.getHours() + 1);
}
d.setMinutes(0);

Answer 5

Or you could mix the two for optimal size. http://jsfiddle.net/HkEZ7/

function roundMinutes(date) {
    return date.getMinutes() >= 30 ? date.getHours() + 1 : date.getHours();
}