by Rick Darnell

Key Differences Between VB and VBScript

You didn't run out to the computer store and buy a copy of VBScript. You didn't install a VBScript disk on your computer, either. All you did was install the Internet Explorer browser, which supports VBScript, on your computer--just like millions of other folks. Everyone of them has the VBScript engine on their computer, and everyone of them has the ability to create Web pages with VBScript.

So where's the integrated development environment that you're used to using in Visual Basic? Keep looking, because there isn't one. All you have is your favorite text editor, the ActiveX Control Pad, and a Web browser. That in itself is the single largest difference between Visual Basic and VBScript. It leads to some specific differences, too. Here's what they are:

• Debugging  VBScript doesn't have a debugger like Visual Basic. You'll resort to using lots of message boxes, instead.
  
  
• Event-handlers  You don't have an editor in which you select an object and event to edit an event-procedure. You have to name event-procedures in your scripts so that the scripting engine can find the appropriate handler when an object fires an event.
  
  
• Forms  VBScript doesn't have a forms editor. It doesn't need one, because you can't display forms anyway. You put forms and controls on the Web page, instead. You can use the ActiveX Control pad to insert all those nasty <OBJECT> tags in your Web page, however.

You don't compile a VBScript program into an EXE file like you do with a Visual Basic program. You distribute your scripts as plain, old text embedded in HTML files. Everyone and his uncle can read your scripts. The script engine interprets this text into intermediate code when it loads the Web page. It also creates a symbol table so that it can quickly look up things such as event-procedures and variable names. The scripting engine uses the ActiveX Scripting technology to interact with the browser.

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[BEG]NOTE:[END] You'll find a plethora of nit-picky differences between Visual Basic and VBScript, too. You have to use the value property to query an objects value, for example. Thus, instead of reading a text box's value using form.text, you have to read it using form.text.value. These subtle differences are too numerous to document in this appendix. Go to Microsoft's Web site (www.microsoft.com) and their knowledge base for further explanation of these differences.

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Another significant difference between Visual Basic and VBScript is the keywords that Microsoft omitted from VBScript. You'll learn more about the keywords included in VBScript in the next section. You'll learn about the keywords that Microsoft omitted from VBScript in "Visual Basic Keywords Omitted from VBScript," later in this appendix.

Visual Basic Keywords Included in VBScript

VBScript includes all the keywords and features that you need to activate a Web page. You can't read or write files, as you'll learn later in this appendix, but you can handle any event that an object fires. You can also handle just about any type of data that you'll find on a Web page and manipulate the Web page in anyway you want.

Table C.1 describes each keyword or feature available in VBScript. I've divided this table into broad categories, with each entry under a category describing a single feature. I've used the same categories that Microsoft uses so that you can keep this information straight as you bounce back and forth between Microsoft's Web site and this book. If you don't find a feature that you expect to see, check out Table C.2 to see if that feature is in the list of Visual Basic features omitted from VBScript.

You can find more information about VBScript's features at Microsoft's VBScript Web site: http://www.microsoft.com/vbscript.

Table C.1  VBScript Keywords

Keyword/Feature	Description
Array handling
IsArray	Returns True if a variable is an array
Erase	Reinitilizes a fixed-size array
LBound	Returns the lower bound of an array
UBound	Returns the upper bound of an array
Assignments
=	Assigns a value to a variable
Let	Assigns a value to a variable
Set	Assigns an object to a variable
Comments
`	Includes inline comments in your script
Rem	Includes comments in your script
Constants/Literals
Empty	Indicates an uninitialized variable
Nothing	Disassociates a variable with an object
Null	Indicates a variable with no data
True	Boolean True
False	Boolean False
Control flow
Do...Loop	Repeats a block of statements
For...Next	Repeats a block of statements
For Each...Next	Repeats a block of statements
If...Then...Else	Conditionally executes statements
Select Case	Conditionally executes statements
While...Wend	Repeats a block of statements
Conversions
Abs	Returns absolute value of a number
Asc	Returns the ASCII code of a character
AscB	Returns the ASCII code of a character
AscW	Returns the ASCII code of a character
Chr	Returns a character from an ASCII code
ChrB	Returns a character from an ASCII code
ChrW	Returns a character from an ASCII code
CBool	Converts a variant to a boolean
CByte	Converts a variant to a byte
CDate	Converts a variant to a date
CDbl	Converts a variant to a double
Cint	Converts a variant to an integer
CLng	Converts a variant to a long
CSng	Converts a variant to a single
CStr	Converts a variant to a string
DateSerial	Converts a variant to a date
DateValue	Converts a variant to a date
Hex	Converts a variant to a hex string
Oct	Converts a variant to an octal string
Fix	Converts a variant to a fixed string
Int	Converts a variant to an integer string
Sgn	Converts a variant to a single string
TimeSerial	Converts a variant to a time
TimeValue	Converts a variant to a time
Dates/Times
Date	Returns the current date
Time	Returns the current time
DateSerial	Returns a date from its parts
DateValue	Returns a date from its value
Day	Returns day from a date
Month	Returns month from a date
Weekday	Returns weekday from a date
Year	Returns year from a date
Hour	Returns hour from a time
Minute	Returns minute from a time
Second	Returns seconds from a time
Now	Returns current date and time
TimeSerial	Returns a time from its parts
TimeValue	Returns a time from its value
Declarations
Dim	Declares a variable
Private	Declares script-level private variable
Public	Declares public-level public variable
ReDim	Reallocates an array
Function	Declares a function
Sub	Declares a subprocedure
Error Handling
On Error	Enables error handling
Err	Contains information about last error
Input/Output
InputBox	Prompts the user for input
MsgBox	Displays a message to the user
Math
Atn	Returns the Arctangent of a number
Cos	Returns the cosine of a number
Sin	Returns the sine of a number
Tan	Returns the tangent of a number
Exp	Returns the exponent of a number
Log	Returns the logarithm of a number
Sqr	Returns the square root of a number
Randomize	Reseeds the randomizer
Rnd	Returns a random number
Operators
+	Addition
-	Subtraction
^	Exponentiation
Mod	Modulus arithmetic
*	Multiplication
/	Division
\	Integer Division
-	Negation
&	String concatenation
=	Equality
<>	Inequality
<	Less Than
<=	Less Than or Equal To
>	Greater Than
>=	Greater Than or Equal To
Is	Compares expressions
And	Compares expressions
Or	Compares expressions
Xor	Compares expressions
Eqv	Compares expressions
Imp	Compares expressions
Objects
CreateObject	Creates reference to an OLE object
IsObject	Returns True if object is valid
Options
Option Explicit	Forces explicit variable declaration
Procedures
Call	Invokes a subprocedure
Function	Declares a function
Sub	Declares a subprocedure
Strings
Instr	Returns index of a string in another
InStrB	Returns index of a string in another
Len	Returns the length of a string
LenB	Returns the length of a string
Lcase	Converts a string to lowercase
Ucase	Converts a string to uppercase
Left	Returns the left portion of a string
LeftB	Returns the left portion of a string
Mid	Returns the mid portion of a string
MidB	Returns the mid portion of a string
Right	Returns the right portion of a string
RightB	Returns the right portion of a string
Space	Pads a string with spaces
StrComp	Compares two strings
String	Pads a string with a character
Ltrim	Removes leading spaces from a string
Rtrim	Removes trailing spaces from a string
Trim	Removes leading and trailing spaces
Variants
IsArray	Returns True if variable is an array
IsDate	Returns True if variable is a date
IsEmpty	Returns True if variable is empty
IsNull	Returns True if variable is null.
IsNumeric	Returns True if variable is a number
IsObject	Returns True if variable is an object
VarType	Indicates a variable's type

Visual Basic Keywords Omitted from VBScript

VBScript leaves out a bunch of Visual Basic keywords such as DoEvents, Print, and Shell. You can't read or write files, either, and you can't do much graphical programming. This won't stop you from creating great Web pages with VBScript, though, because VBScript provides every feature you need to do just about anything you want on the Web page. For example, you can dynamically change the contents of the Web page itself and you can interact with every object on the Web page.

Don't look at the list of omitted keywords and features yet. You need to understand why Microsoft didn't include them so that you'll understand why each feature is on this list. Take a look:

• Portability  Microsoft intends to make VBScript available on a variety of platforms including Windows, Mac, UNIX, and so on. They've wisely removed keywords and features that make VBScript less portable to these platforms.
  
  
• Performance  You've heard it before: speed or features--pick one. Microsoft removed many nonessential features from VBScript so scripts load and run faster.
  
  
• Safety  You should be concerned with security on the Internet. You don't want to open a Web page and discover that it contains a script which crashes your drive, do you? Microsoft removed any Visual Basic feature that might cause a security problem with scripts such as file I/O. You can still get access to these features, however, if you create an ActiveX object which you control with VBScript.

Table C.1 describes each keyword or feature available in Visual Basic but omitted from VBScript. I've divided this table into broad categories, with each entry under a category describing a single feature. I've used Microsoft's categories so that you can keep the list on Microsoft's Web site in sync with this list.

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NOTE: The Internet Explorer Script Error dialog box tells you that it found a statement in your script which couldn't interpret. I'm sure that you've seen error messages such as "Expected while or until" or nested comments that just don't make any sense. When VBScript encounters a keyword it doesn't recognize, it spews out all sorts of garbage like the previous example. It usually points to the offending keyword, however, by placing a caret (^) directly underneath it. The next time you get one of these unexplained errors, look up the keyword in Table C.2 to see if Microsoft omitted it from VBScript.

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Table C.2  Visual Basic Keywords Not in VBScript

Keyword/Feature	Description
Array Handling
Option Base	Declares default lower bound
Arrays with lower bound <> 0	All arrays must have 0 lower bound
Clipboard
Clipboard object	Provides access to the clipboard
Clear	Clears the contents of the clipboard
GetFormat	Determines format of clipboard object
GetData	Returns data from the clipboard
SetData	Stores data in the clipboard
GetText	Returns text from the clipboard
SetText	Stores text in the clipboard
Collection
Add	Adds an item to a collection
Count	Returns number of items in collection
Item	Returns an item from a collection
Remove	Removes an item from a collection
Access collections using ! character	Accesses a collection with !
Conditional Compilation
#Const	Defines a compiler constant
#If...Then...#Else	Conditional compilation
Constants/Literals
Const	Defines a constant
All intrinsic	Predefined constants such as vbOK constants
Exponent-based	Real numbers using exponents real number
Trailing data type characters	Defines data types implicitly
Control Flow
DoEvents	Yields execution to Windows
GoSub...Return	Branches to a label in a procedure
GoTo	Goes to a label in a procedure
On Error GoTo	Goes to a label on an error
On...GoSub	Branches to a label on an index
On...GoTo	Goes to a label on an index
Line numbers	Line numbers
Line labels	Labels define GoTo/GoSub targets
With...End With	Provides easy access to an object
Conversion
Chr$	Returns a character from an ASCII code
Hex$	Returns string hex from a number
Oct$	Returns string octal from a number
Ccur	Converts expression to currency
Cvar	Converts expression to a variant
CVDate	Converts an expression to a date
Format	Formats a string
Format$	Formats a string
Str	Returns a string form of a number
Str$	Returns a string form of a number
Val	Returns a number from a string
Data Types
All intrinsic data types except variant	Data types such as Date
Type...End Type	Defines user-defined data type
Date/Time
Date statement	Returns the current date
Time statement	Returns the current time
Date$	Returns the current date
Time$	Returns the current time
Timer	Returns seconds elapsed since midnight
DDE
LinkExecute	Sends command during DDE conversation
LinkPoke	Sends data during a DDE conversation
LinkRequest	Receives data during DDE conversation
LinkSend	Sends data during a DDE conversation
Debugging
Debug.Print	Prints to the debugging window
End	Shuts down the application
Stop	Stops the application
Declaration
Declare	Declares a DLL
Property Get	Defines a user-defined class
Property Let	Defines a user-defined class
Property Set	Defines a user-defined class
Public	Declares a public variable
Private	Declares a private variable
ParamArray	Accepts a variable number of arguments
Optional	Specifies an optional argument
New	Creates a new object
Error Handling
Erl	Returns the line number of an error
Error	Returns an error message
Error$	Returns an error message
On Error...Resume	Enables error handling
Resume	Resumes after an error
Resume Next	Resumes after an error
File Input/Output
All	Opens, reads, writes, and closes files
Financial
All financial	Financial function such as Rate functions.
Graphics
Cls	Clears the screen
Circle	Draws a circle
Line	Draws a line
Point	Draws a point
Pset	Changes a point's color
Scale	Defines the coordinate system
Print	Prints to a file
Spc	Position output using Print
Tab	Inserts a tab character
TextHeight	Returns height of a text string
TextWidth	Returns width of a text string
LoadPicture	Loads a picture from disk
SavePicture	Saves a picture to disk
QBColor	Returns an RGB color code
RGB	Combines RGB color codes
Manipulating Objects
Arrange	Arranges windows
Zorder	Changes z-order of windows
SetFocus	Sets focus to a window
InputBox$	Prompts the user for a string
Drag	Begins a drag-and-drop operation
Hide	Hides a form
Show	Shows a form
Load	Loads a form
Unload	Unloads a form
Move	Moves a form
PrintForm	Prints a form
Refresh	Repaints a form
AddItem	Adds item to list box
RemoveItem	Removes item from a list box
Miscellaneous
Environ	Returns the user's environment
Environ$	Returns the user's environment
SendKeys	Sends keystrokes to a window
Command	Returns the command line parameters
Command$	Returns the command line parameters
AppActivate	Activates an application's window
Shell	Launches another program
Beep	Beeps the speaker
Object Manipulation
GetObject	Returns an OLE object from a file
TypeOf	Returns the type of an object
Operators
Like	Compares to strings
Options
def type	Sets default data type for variables
Option Base	Sets default lower bound for arrays
Option Compare	Defines default comparison method
Option Private	Defines default scope module
Printing
TextHeight	Returns height of a text string
TextWidth	Returns width of a text string
EndDoc	Terminates a print operation
NewPage	Ejects the current page
PrintForm	Prints a form
Strings
All fixed-length	Strings with a fixed length
LCase$	Converts a string to lowercase
UCase$	Converts a string to uppercase
Lset	Left-aligns a string
Rset	Right-aligns a string
Space$	Pads a string with spaces
String$	Pads a string with a character
Format	Formats a string
Format$	Formats a string
Left$	Returns left portion of a string
Mid$	Returns middle portion of a string
Right$	Returns right portion of a string
Mid Statement	Replaces a portion of a string
Trim$	Removes leading and trailing spaces
LTrim$	Removes leading spaces from a string
RTrim$	Removes trailing spaces from a string
StrConv	Performs various conversions
Using Classes
TypeName	Defines a user-defined class
Optional Arguments
IsMissing	Indicates missing optional argument

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