The previous code displays an alert with the number of seconds between 00:00:00 UTC on January 1, 1970 and 00:00:00 UTC on October 28, 2007.
How it works:
UTC is a static method of the Date object. The complete signature of this method is the following:
UTC(year, month, [day], [hours], [minutes], [seconds], [milliseconds])
Note that the parameters between square brackets are optional. The UTC method returns the number of milliseconds using UTC (Universal Time Coordinated). Hence the following code:
computes the number of seconds between 00:00:00 UTC on January 1, 1970 and 00:00:00 UTC on October 28, 2007. Note that the month parameter ranges from 0 (Jan) to 11 (Dec).