🗝️ ASP – VB Keywords – Essential VBScript Reserved Words for Classic ASP

🧲 Introduction – What Are VB Keywords in Classic ASP?

VBScript keywords (also called reserved words) are predefined words in the VBScript language used by Classic ASP. These words are part of the language syntax and cannot be used as variable names or identifiers. Understanding these keywords is essential for writing valid and functional ASP pages.

🎯 In this guide, you’ll learn:

• The list of built-in VBScript keywords used in Classic ASP
• Their purposes and typical use cases
• Code examples for each major keyword group
• Common mistakes and best practices

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🗂️ Categories of VBScript Keywords

VBScript keywords in Classic ASP can be grouped as follows:

Category	Examples
Control Flow	If, Else, Select, Case, For, Next, While, Do, Loop, Exit
Declarations	Dim, Const, Function, Sub, Call, Set
Operators	And, Or, Not, Mod, Is, Like
Error Handling	On Error Resume Next, Err, IsObject
Type & Value	Nothing, True, False, Empty, Null
Miscellaneous	Option Explicit, ByVal, ByRef, Class, New

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🔄 Control Flow Keywords

These control logic and decision-making in ASP.

<%
Dim age
age = 22

If age >= 18 Then
    Response.Write "Adult"
Else
    Response.Write "Minor"
End If
%>

Keyword	Purpose
If	Starts a conditional block
Then	Executes block if condition true
Else	Defines alternate logic
Select Case	Multibranch condition
For, Next	Looping structure
Do, While, Loop	Conditional loops

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🧱 Declaration Keywords

Used to declare variables, constants, functions, and procedures.

<%
Dim name
Const MAX = 10

Function Add(x, y)
    Add = x + y
End Function
%>

Keyword	Purpose
Dim	Declare variables
Const	Define constants
Function	Define a function that returns value
Sub	Define a procedure
Set	Assign an object reference
Call	Call a subroutine (optional)

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⚙️ Operators & Logical Keywords

<%
Dim a, b
a = 10
b = 20

If a < b And b < 100 Then
    Response.Write "Valid range"
End If
%>

Keyword	Purpose
And	Logical AND
Or	Logical OR
Not	Logical negation
Mod	Modulus operator (remainder)
Is	Compare objects
Like	Pattern matching in strings

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🛑 Error Handling Keywords

<%
On Error Resume Next
Dim result
result = 10 / 0 ' No error displayed
If Err.Number <> 0 Then
    Response.Write "An error occurred: " & Err.Description
End If
%>

Keyword	Purpose
On Error Resume Next	Suppresses runtime error messages
Err	Error object for handling exceptions
IsObject	Checks if a variable is an object

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💡 Type & Value Constants

<%
Dim status
status = Null

If IsNull(status) Then
    Response.Write "Status is unknown"
End If
%>

Keyword	Purpose
Null	Represents no valid data
Empty	Uninitialized variable
Nothing	No object is assigned
True	Boolean true
False	Boolean false

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⚠️ Miscellaneous Keywords

Option Explicit
Dim total
total = 100

Keyword	Purpose
Option Explicit	Forces variable declaration with Dim
ByVal / ByRef	Defines parameter passing method
Class	Begin class definition
New	Create object instances

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📘 Best Practices for VB Keywords

✅ Do:

• Always use Option Explicit for clean code
• Use Dim to declare all variables explicitly
• Apply logical operators carefully in conditions

❌ Avoid:

• Overwriting keywords as variable names
• Skipping Set when assigning object variables
• Using On Error Resume Next without checking Err afterward

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📌 Summary – Recap & Next Steps

VBScript keywords are the building blocks of Classic ASP scripting. They define structure, logic, and control, making your server-side code predictable, readable, and robust.

🔍 Key Takeaways:

• Keywords include If, Dim, Function, Err, Set, Nothing, etc.
• Reserved words cannot be used as variable names
• Use them to control flow, declare data, and handle errors effectively

⚙️ Real-world Use Cases:

• Structuring login logic
• Declaring constants for configurations
• Handling errors in data processing routines

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❓ FAQs – ASP VB Keywords

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❓ Can I use VB keywords as variable names?
❌ No. Reserved words like If, Function, Set, etc., cannot be used as variable names.

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❓ Is VBScript case-sensitive?
✅ No. VBScript in Classic ASP is not case-sensitive.

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❓ What’s the difference between Null and Nothing?
✅ Null is for data values, while Nothing is for object references.

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