How do I get the difference between two Dates in JavaScript?

Question

I\'m creating an application which lets you define events with a time frame. I want to automatically fill in the end date when the user selects or changes the start date.

Answer 1

Thanks @Vincent Robert, I ended up using your basic example, though it's actually newBegin + oldEnd - oldBegin. Here's the simplified end solution:

    // don't update end date if there's already an end date but not an old start date
    if (!oldEnd || oldBegin) {
        var selectedDateSpan = 1800000; // 30 minutes
        if (oldEnd) {
            selectedDateSpan = oldEnd - oldBegin;
        }

       newEnd = new Date(newBegin.getTime() + selectedDateSpan));
    }