How do I subtract minutes from a date in JavaScript?

Question

Once you know this:

You can create a Date by calling the constructor with milliseconds since Jan 1, 1970.
The valueOf() a Date is the number of milliseconds since Jan 1, 1970
There are 60,000 milliseconds in a minute :-]

In the code below, a new Date is created by subtracting the appropriate number of milliseconds from myEndDateTime:

var MS_PER_MINUTE = 60000;
var myStartDate = new Date(myEndDateTime - durationInMinutes * MS_PER_MINUTE);