一天中的新JavaScript日期对象

Question

Seems simple but I can't figure it out. sigh

I have 74141 as seconds in a day, how do I create a Date object from this number to represent the time in hours and seconds? The actual date I don't care about because I'm just going to be using getHours/Seconds/Minutes to set another date which has the correct date.

Answer 1

You can use Date.prototype.setSeconds for this purpose. You don't really need to worry about conversion, as that is automatic:

var date = new Date(1970, 0, 1); 
date.setSeconds(secs);

The above trick relies on the fact that the Date points exactly to midnight, so the timing you get back is precise. For precision reasons, I am using EPOCH, although any "exact" midnight would do.

Answer 2

1. Get the date

     var now = new Date(); 

2. Zero out the time-of-day fields:

     now.setHours(0).setMinutes(0).setSeconds(0).setMilliseconds(0); 

3. Create a new time from your time-of-day number:

     var theTime = new Date(now.getTime() + timeInSeconds * 1000); 

You could of course use a Date instance representing any other date, but it seems like using the current date would be the least weird thing to do (barring some other conditions).

edit — actually after zeroing out the time fields, you could just use .setSeconds() with your value and avoid creating a new object. It's probably not a big issue one way or the other.

Answer 3

In addition to alex23's answer, it's enough to give 0 as date construction param.

var date = new Date(1970, 0, 1);
// same as
var date = new Date(0);