Flash actionscript date time

How to Create Date objects

The Date() constructor returns a Date object containing the current date and time, in local time based on your time zone. Here’s an example:

var now:Date = new Date();

2nd example,The Date() constructor treats that as the number of milliseconds since January 1, 1970,
and returns a corresponding Date object. Note that the millisecond value you pass in is treated as milliseconds since January 1, 1970, in UTC. However, the Date object shows values in your local time zone, unless you use the UTC-specific methods to retrieve and display them. If you create a new Date object using a single milliseconds parameter,
make sure you account for the time zone difference between your local time and UTC.
The following statements create a Date object set to midnight on the day of January 1, 1970, in UTC:

var millisecondsPerDay:int = 1000 * 60 * 60 * 24;
// gets a Date one day after the start date of 1/1/1970
var startTime:Date = new Date(millisecondsPerDay);

3 rd example, you can pass multiple numeric parameters to the Date() constructor. It treats those parameters as the year, month, day, hour, minute, second, and millisecond, respectively, and returns a corresponding Date object. Those input parameters are assumed to be in local time rather than UTC. The following statements get a Date object set to midnight at the start of January 1, 2000, in local time:
var millenium:Date = new Date(2000, 0, 1, 0, 0, 0, 0);

Get time unit values
You can extract the values for various units of time within a Date object using properties or methods of the Date class. Each of the following properties gives you the value of a time unit in the Date object:


The fullYear property
The month property, which is in a numeric format with 0 for January up to 11 for December
The date property, which is the calendar number of the day of the month, in the range of 1 to 31
The day property, which is the day of the week in numeric format, with 0 standing for Sunday
The hours property, in the range of 0 to 23
The minutes property
The seconds propert

In fact, the Date class gives you a number of ways to get each of these values. For example, you can get the month value of a Date object in four different ways:

The month property
The getMonth() method
The monthUTC property
The getMonthUTC() method
All four ways are essentially equivalent in terms of efficiency, so you can use whichever approach suits your application best.
The properties just listed all represent components of the total date value. For example, the milliseconds property will never be greater than 999, since when it reaches 1000 the seconds value increases by 1 and the milliseconds property resets to 0.
If you want to get the value of the Date object in terms of milliseconds since January 1, 1970 (UTC), you can use the getTime() method. Its  counterpart, the setTime() method, lets you change the value of an existing Date object using milliseconds since January 1, 1970 (UTC).
The milliseconds property



Performing date and time arithmetic
You can perform addition and subtraction on dates and times with the Date class. Date values are kept internally in terms of  milliseconds, so you should convert other values to milliseconds before adding them to or subtracting them from Date objects.

If your application will perform a lot of date and time arithmetic, you might find it useful to create constants that hold common time unit values in terms of milliseconds, like the following:
public static const millisecondsPerMinute:int = 1000 * 60;
public static const millisecondsPerHour:int = 1000 * 60 * 60;
public static const millisecondsPerDay:int = 1000 * 60 * 60 * 24;
Now it is easy to perform date arithmetic using standard time units. The following code sets a date value to one hour from the current time using the getTime() and setTime() methods:

var oneHourFromNow:Date = new Date();

oneHourFromNow.setTime(oneHourFromNow.getTime() + millisecondsPerHour);
Another way to set a date value is to create a new Date object using a single milliseconds parameter. For example, the following code adds 30 days to one date to calculate another:

// sets the invoice date to today's date

var invoiceDate:Date = new Date(); 
// adds 30 days to get the due date
var dueDate:Date = new Date(invoiceDate.getTime() + (30 * millisecondsPerDay));
Next, the millisecondsPerDay constant is  multiplied by 30 to represent 30 days’ time and the result is added to the invoiceDate value and used to set the dueDate value.



Convert  between time zones
Date and time arithmetic comes in handy when you want to convert dates from one time zone to another. So does the getTimezoneOffset() method, which  returns the value in minutes by which the Date object’s time zone differs from UTC. It returns a value in minutes because not all time zones are set to even-hour increments—some have half-hour offsets from neighboring zones.

The following example uses the time zone offset to convert a date from local time to UTC. It does the conversion by first calculating the time zone value in milliseconds and then adjusting the Date value by that amount:

// creates a Date in local time
var nextDay:Date = new Date("Mon May 1 2006 11:30:00 AM"); 

// converts the Date to UTC by adding or subtracting the time zone offset
var offsetMilliseconds:Number = nextDay.getTimezoneOffset() * 60 * 1000;
nextDay.setTime(nextDay.getTime() + offsetMilliseconds);