VBScript Keywords

Keyword&Description
-----------------------
empty(Keyword):
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:
dim x 'the variable x is uninitialized!
x="ff" 'the variable x is NOT uninitialized anymore
x=empty 'the variable x is uninitialized!

Note: This is not the same as Null!!

isEmpty(Keyword):
Used to test if a variable is uninitialized.
Example: If (isEmpty(x)) 'is x uninitialized?

is nothing(Keyword):
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(Keyword):
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(Keyword):
Used to test if a value contains invalid data.
Example: if (isNull(x)) 'is x invalid?

true(Keyword):
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)