I have two date variable separately like following

startDate is a Date instance with the value Tue Jul 17 2012 00:00:00 GMT+0530 (IST)

startTime is a String with the value "11:30 AM"

Now what I need is join of both above date & time, as a Date.

startDateTime = Tue Jul 17 2012 11:30:00 GMT+0530 (IST)

I tried

new Date(startDate + " " + startDate) but outputting invalid date.

Also tried the way shown on this post. But still not working.

I have two date variable separately like following

startDate is a Date instance with the value Tue Jul 17 2012 00:00:00 GMT+0530 (IST)

startTime is a String with the value "11:30 AM"

Now what I need is join of both above date & time, as a Date.

startDateTime = Tue Jul 17 2012 11:30:00 GMT+0530 (IST)

I tried

new Date(startDate + " " + startDate) but outputting invalid date.

Also tried the way shown on this post. But still not working.

• javascript
• datetime

• Have you tried date.js javascript library? It can convert/parse a lot of date formats. – Jonas T Commented Jul 20, 2012 at 10:02
• 1 Are startDate and startTime strings? – Lucero Commented Jul 20, 2012 at 10:03
• 2 @JonasT, or moment.js, which I prefer. – Lucero Commented Jul 20, 2012 at 10:04
• moment.js has the advantage of having been maintained in the last few years, which DateJS has not. – T.J. Crowder Commented Jul 20, 2012 at 10:04
• 1 @RikeshShah: To improve a question, use the "edit" link underneath it. I've done that for you on this occasion. – T.J. Crowder Commented Jul 20, 2012 at 10:07

3 Answers 3

You can readily parse startTime if it's in a clearly-defined format, then use setHours and setMinutes: Live example | source

var startDateTime;
var parts = /^(\d+):(\d+) (AM|PM)$/.exec(startTime);
if (parts) {
    hours = parseInt(parts[1], 10);
    minutes = parseInt(parts[2], 10);
    if (parts[3] === "PM" && hours !== 12) {
        hours += 12;
    }
    else if (parts[3] === "AM" && hours === 12) {
        hours = 0;
    }
    if (!isNaN(hours) && !isNaN(minutes)) {
        startDateTime = new Date(startDate.getTime());
        startDateTime.setHours(hours);
        startDateTime.setMinutes(minutes);
    }
}

...or something along those lines.

Note that key to this is the fact you've said startDate is a Date instance. The above assumes we're working within the timezone of the JavaScript environment, not across zones. If you were starting with a date string instead, and that string specified a timezone other than the JavaScript environment's timezone, which you were then converting into a Date via new Date("Tues Jul...."), then you'd have to be sure to adjust the resulting Date to use either the local time of the environment, or UTC; if you adjusted it to be UTC, you'd use setUTCHours and setUTCSeconds above instead of setHours and setSeconds. Again, this is only an issue if your starting point is a date string, and that string specifies a timezone different from the timezone in which the code above is running.

You can do This:

var theDate = new Date("Tue Jul 17 2012 00:00:00 GMT+0530 (IST)");
var theTime = "11:30 AM";
var hours = theTime .substr(0,2);
var minutes = theTime .substr(3,2);
var amOrPm = theTime .substr(6,2);
if (hours < 12 && "PM" == amOrPm) {
    hours = +hours + 12;
}
theDate.setHours(hours);
theDate.setMinutes(minutes);

Try

new Date(startDate.toDateString() + " " + startTime)

This bines the date string from your Date object with the time string, and should give you a valid date. Note that this ignores the timezone you initially worked with, you might need to add " GMT+0530" again.

However, because your date string is already timezone-biased (Jul 16 2012, 20:30:00 UTC) it might be better to add them together, i.e. like new Date(+startDate + milliseconds):

var startDate = new Date("Tue Jul 17 2012 00:00:00 GMT+0530");
var startTime = "11:30 AM";
return new Date(+startDate + +new Date("1 1 1970 "+startTime))