Calculating the time within a day uses modulo arithmetic to find the remainder after calculating the day number.

The formula for calculating time within the day is shown here:

• t = an instant in time measured in milliseconds relative to 01-January-1970 UTC.

• msPerDay = 86400000

• TimeWithinDay(t) = t modulo msPerDay

Example code:

   // Define some constants

   HoursPerDay      =   24;

   MinutesPerHour   =   60;

   SecondsPerMinute =   60;

   msPerSecond      = 1000;

   

   // Derived values

   msPerMinute = msPerSecond * SecondsPerMinute;

   msPerHour   = msPerMinute * MinutesPerHour;

   msPerDay    = msPerHour   * HoursPerDay;

   

   // Grab the time now in milliseconds

   myMilliseconds = Number(new Date());

   document.write("Time within day ...: ");

   document.write(TimeWithinDay(myMilliseconds));

   document.write("<BR>");

   

   // Work out the millisecond time value

   function TimeWithinDay(aMillisecondTime)

   {

      return (aMillisecondTime % msPerDay);

   }

Cross-references:

ECMA 262 edition 2 - section - 15.9.1.2

ECMA 262 edition 3 - section - 15.9.1.2