Has a session variable been created?

How do you test if a session variable has been created? I assume it is

VB Code:

session("alert")=null

Is this a correct way of doing it?

I'm not sure of the "right way" for that.

But I use this:

VB Code:

<%
If Len(Session("alert")) > 0 Then
Response.Write "alert session does exist"
End If
%>

And, the right way to check if it's null goes with "IsNull" function:

VB Code:

If Not IsNull(anyVariable) Then
Response.Write "anyVariable is not null, but it could be empty"
End If

Anyway, here is the result I got after a few tests:

Code:

---

variable / session              IsNull          IsEmpty          Len = 0
Not Declared / Created          false            true              true
= ""                            false            false            true
= Null                          true            false            true
= Empty                          false            true              true
= "anything"                    false            false            false

---

That means, if you check for Null, Empty or Len(var) = 0 of a variable right on the first line of the file (before anything else, including declarations, etc), you'll get the results on the first line. And it works for session as well, since they're treated as variables.