Recipe 14.1. Finding the Current Date and Time

Problem

You want to know the current date and time.

Solution

Create a new date by using the Date( ) constructor with no parameters. Alternatively, use a CGI script or any other server-side program to return the server time and create a new Date object from that value.

Discussion

The date and time that ActionScript calculates on its own is based on the client computer's date and time settings. Therefore, if the user's computer has the incorrect time, so will the Date object. With that caveat in mind, you can retrieve the current client-side date and time by creating a new Date object by using a constructor without parameters, as follows:

// Create a new Date object. var current:Date = new Date(  ); // Displays client-side date and time. trace(current);

If you have an Internet connection, the Flash movie attempts to retrieve the date and time from a server. This technique can ensure more accurate dates and times. Although the server's time settings might be inaccurate, at least the time will be consistent for all clients.

The basic process when reading the time from a server is as follows:

Create a CGI script on the web server that outputs the number of seconds since midnight of January 1, 1970 (the epoch).
Use a flash.net.URLLoader object from ActionScript to load the epoch seconds.
Convert the loaded seconds from a string to a number, multiply by 1,000, and construct a new Date object by passing the value to the constructor.

PHP is a scripting language that can be found on a large number of web hosts. It is quite simple to create a PHP page to output the current time and date as the number of seconds since the epoch. All you need to do is create a PHP document with the following content and upload it to the server:

<?php echo time(  );?>

If you don't have PHP on your server, or if you are simply more comfortable with Perl (another language that is almost universally available on web servers), then here is a Perl script that outputs the number of seconds since the epoch:

#!/usr/local/bin/perl print "Content-type:text/plain\n\n"; print time;

There are a few tips to keep in mind when setting up this script on your server:

The first line indicates where the Perl interpreter can be found. The value given in the example is fairly universal. However, contact your web server administrator if you encounter problems.
Many servers disable remote script execution without particular file extensions; however, the .cgi extension is commonly allowed. Try renaming the script getDate.cgi.
Most web servers limit CGI access to specific directories. These directories are normally found in the account's root directory (or within the web root of the account), and are named either cgi or cgi-bin. Make sure you save the script in the correct directory.
On Unix servers, your CGI script must have its permissions set to 755. Most FTP programs allow you to change permissions. If you are working from a shell script, use the following command:

                      chmod 755 filename

Regardless of what server-side language you use, you need to load the time value from the server using ActionScript. You can accomplish that by using a flash.net.URLLoader object.

If you pass the Date constructor a single value, ActionScript interprets it as the number of milliseconds since the epoch and creates a new Date object that corresponds to that value. Therefore, you must multiply the value returned by the script (which is in seconds) by 1,000; for example:

package {   import flash.net.URLLoader;   import flash.net.URLRequest;   import flash.events.Event;   public class ServerDateTimeExample {     public function ServerDateTimeExample(  ) {       // The following code constructs a URLLoader object, adds        // an event listener so that the onDateTimeLoad(  ) method is       // called when the data loads, and then it makes the request       // to the server script.       var loader:URLLoader = new URLLoader(  );       loader.addEventListener(Event.COMPLETE, onDateTimeLoad);       loader.load(new URLRequest("script.cgi"));     }     private function onDateTimeLoad(event:Event):void {       var loader:URLLoader = URLLoader(event.target);       var data:int = parseInt(loader.data);       var current:Date = new Date(data * 1000);       trace(current);     } }

The date is always stored in ActionScript as the milliseconds since the epoch, and it is always displayed with proper offsets, based on the user's local time zone setting (unless you specifically use the UTC methods). So, if the user's computer has the incorrect time zone setting, the display might be incorrect. However, the actual date (as stored in epoch milliseconds) is still correct.

Problem

Solution

Discussion

See Also