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Actionscript Cookbook by Joey Lott

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10.6. Calculating Elapsed Time or Intervals Between Dates

Problem

You want to calculate an elapsed time, elapsed date, or relative time.

Solution

For simple elapsed time, add and subtract from the Epoch milliseconds or the value returned by getTimer( ). For more complex conversions, create custom Date.doMath( ) and Date.elapsedTime( ) methods.

Discussion

For simple conversions such as adding or subtracting an hour, day, or week to or from a date, simply add or subtract from the date’s Epoch milliseconds value. For this purpose, note that a second is 1,000 milliseconds, a minute is 60,000 milliseconds, an hour is 3,600,000 milliseconds, a week is 604,800,000 milliseconds, and so on. Unless you have a spectacular gift for remembering these conversion values, storing them as constants of the Date class is the easiest option. You can add the following constants to your Date.as file for convenience:

// There are 1000 milliseconds in a second, 60 seconds in a minute, 60 minutes in an
// hour, 24 hours in a day, and 7 days in a week.
Date.SEC  = 1000;
Date.MIN  = Date.SEC * 60;
Date.HOUR = Date.MIN * 60;
Date.DAY  = Date.HOUR * 24;
Date.WEEK = Date.DAY * 7;

You can use the Date.getTime( ) method to retrieve a date’s current value in Epoch milliseconds, and you can set the new value using the Date.setTime( ) method. The following example adds one day to a given Date object.

#include "Date.as" myDate = new Date(1978, 9, 13, 3, 55, 0, 0); // Displays: Fri Oct 13 03:55:00 GMT-0700 1978 trace(myDate); ...

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