Question

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.

Answer 1

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.