The ECMA standard defines some useful methods for decomposing time values.

Some constant values need to be defined first:

• HoursPerDay = 24

• MinutesPerHour = 60

• SecondsPerMinute = 60

• msPerSecond = 1000

From these we can derive some other values:

• msPerMinute = msPerSecond * SecondsPerMinute = 60000

• msPerHour = msPerMinute * MinutesPerHour = 3600000

Now the methods can be defined in terms of these constants and their derivatives.

• HourFromTime(t) = floor(t / msPerHour) modulo HoursPerDay

• MinFromTime(t) = floor(t / msPerMinute) modulo MinutesPerHour

• SecFromTime(t) = floor(t / msPerSecond) modulo SecondsPerMinute

• msFromTime(t) = t modulo msPerSecond

Example code:

   // Define some constants

   HoursPerDay      =   24;

   MinutesPerHour   =   60;

   SecondsPerMinute =   60;

   msPerSecond      = 1000;

   

   // Derived values

   msPerMinute = msPerSecond * SecondsPerMinute;

   msPerHour   = msPerMinute * MinutesPerHour;

   

   // Grab the time now in milliseconds

   myMilliseconds = Number(new Date());

   document.write("Hours ...: ");

   document.write(HourFromTime(myMilliseconds));

   document.write("<BR>");

   document.write("Minutes ...: ");

   document.write(MinFromTime(myMilliseconds));

   document.write("<BR>");

   document.write("Seconds ...: ");

   document.write(SecFromTime(myMilliseconds));

   document.write("<BR>");

   document.write("Milliseconds ...: ");

   document.write(msFromTime(myMilliseconds));

   document.write("<BR>");

   

   // Work out the hour number (Add 1 hour for BST)

   function HourFromTime(aMillisecondTime)

   {

      return (Math.floor(aMillisecondTime/msPerHour) % HoursPerDay);

   }

   

   // Work out the minutes of the hour

   function MinFromTime(aMillisecondTime)

   {

      return (Math.floor(aMillisecondTime/msPerMinute) % MinutesPerHour);

   }

   

   // Work out the seconds of the minute

   function SecFromTime(aMillisecondTime)

   {

      return (Math.floor(aMillisecondTime/msPerSecond) % SecondsPerMinute);

   }

   

   // Work out the millisecond time value

   function msFromTime(aMillisecondTime)

   {

      return (aMillisecondTime % msPerSecond);

   }

Cross-references:

ECMA 262 edition 2 - section - 15.9.1.10

ECMA 262 edition 3 - section - 15.9.1.10