In an ASP application,the Global.asa file is an optional file that stores declarations of objects, variables, and methods that can be accessed by every page . Global.asa file uses all valid browser scripts (JavaScript, VBScript, JScript, PerlScript, etc.) The Global.asa file stores only the following:

• Application events
• Session events
• <object> declarations 
• TypeLibrary declarations
• the #include directive

Note: Each application can only have one Global.asa file and the Global.asa file must be stored in the root directory of the ASP application.

when the application/session starts or application/session ends ,it is necessary to tell the application and session objects in Glogal.asa about the work to be done. The code for this is placed in event handlers. The Global.asa file uses four types of events:

Application_OnStart - This event occurs in an ASP application when the FIRST user calls the first page from . This event occurs after the Global.asa file is edited or after the Web server is restarted. The "Session_OnStart" event occurs immediately after this event.

Session_OnStart - In the ASP application,this event occurs EVERY time a NEW user requests his or her first page .

Session_OnEnd - EVERY time a user ends a session, this event occurs. After a page has not been requested by the user for a specified time (by default this is 20 minutes),a user ends a session .

Application_OnEnd - Aafter the LAST user has ended the session,this event occurs. Typically, this event occurs when a Web server stops. To clean up settings after the Application stops,this procedure is used like delete records or write information to text files.

A Global.asa file could look something like this:

Because to insert scripts in the Global.asa file we cannot use the ASP script delimiters (<% and %>), we put subroutines inside an HTML <script> element

With the help of <object> tag it is possible to create objects with session or application scope in Global.asa .

Note: The <object> tag should be outside the <script>tag

The first example creates an object of session scope named "MyCreate" by using the ProgID parameter:

The second example creates an object of application scope named "MyConnection" by using the ClassID parameter:

A TypeLibrary is a container that stores DLL file corresponding to a COM object. By including a call to the TypeLibrary in the Global.asa file, the constants of the COM object can be accessed, and errors can be better reported by the ASP code. You can declare the type libraries in Global.asa if your Web application relies on COM objects that have declared data types in type libraries,

The following error messages can return by the server :

In the Global.asa file, METADATA tags can appear anywhere (both inside and outside <script> tags). However, it is recommended that METADATA tags appear near the top of the Global.asa file.

• The text that is written in the Global.asa file can not be displayed. This file can't display information

• in the Application_OnStart and Application_OnEnd subroutines,you can only use Server and Application objects . In the Session_OnEnd subroutine, you can use Server, Application, and Session objects. You can use any built-in object in the Session_OnStart subroutine

To initialize variables.  Global.asa is often used.

The example below shows how to detect the exact time a visitor first arrives on a Web site. The time is stored in a Session variable named "started", and in the application,the value of the "started" variable can be accessed from any ASP page :

To control page access, Global.asa can also be used .

The example below shows how to redirect every new visitor to another page, in this case to a page called "newpage.asp":

In the example below when the Web server starts,the Application_OnStart subroutine occurs . Then the Application_OnStart subroutine calls another subroutine named "getusers". The "getusers" subroutine opens a database and retrieves a record set from the "users" table. The record set is assigned to an array, where it can be accessed from any ASP page without querying the database

In this example we will create a Global.asa file that counts the number of current visitors.

• When the server starts,the Application_OnStart sets the Application variable "visitors" to 0

• Every time a new visitor arrives,the Session_OnStart subroutine adds one to the variable "visitors"

• The Session_OnEnd subroutine subtracts one from "visitors" each time this subroutine is triggered

The Global.asa file: