I found this helpful.
Keyword | Description |
---|---|
Empty | Used to indicate an uninitialized variable value. A variable value is uninitialized when it is first created and no value is assigned to it, or when a variable value is explicitly set to empty.
Example: Note: This is not the same as Null!! |
IsEmpty | Used to test if a variable is uninitialized.
Example: If (IsEmpty(x)) ‘is x uninitialized? |
Nothing | Used to indicate an uninitialized object value, or to disassociate an object variable from an object to release system resources.Example: Set myObject=Nothing |
Is Nothing | Used to test if a value is an initialized object.Example: If (myObject Is Nothing) ‘is it unset?
Note: If you compare a value to Nothing, you will not get the right result! Example: If (myObject = Nothing) ‘always false! |
Null | Used to indicate that a variable contains no valid data.One way to think of Null is that someone has explicitly set the value to “invalid”, unlike Empty where the value is “not set”.
Note: This is not the same as Empty or Nothing!! Example: x=Null ‘x contains no valid data |
IsNull | Used to test if a value contains invalid data.Example: if (IsNull(x)) ‘is x invalid? |
True | Used to indicate a Boolean condition that is correct (True has a value of -1) |
False | Used to indicate a Boolean condition that is not correct (False has a value of 0) |
source:
http://www.w3schools.com/vbscript/vbscript_ref_keywords.asp