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Server-Side Web Programming

with Active Server Pages

VBScript Overview

What is VBScript?

•^

VBScript is a subset of the language "Visual Basic forApplications" (VBA).

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Included in the Windows Script add-in for Windows9x, NT, and 2000.^ –

http://www.microsoft.com/msdownload/vbscript/scripting.asp

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VBA and its derivatives form Microsoft's keylanguage strategy. Learn VB once and you can use itthroughout the Microsoft universe.

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VBScript has some annoying differences.

Language Features Overview

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Declaration^ –

Dim, Const

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Operators and Inequality^ –

+, -, *, &, and, or

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Decision^ –

If, Select, Loops

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Built-in Functions

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User defined routines

Declaration - I

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All variables in VBScript are of type Variant,e.g., they can assume any value.

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Syntax:

Dim myVar

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Good nomenclature and style^ –

One per line with a comment after it

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'starts a comment

Give good descriptive names

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E.g.

Dim TotalSales

not

Dim T

Declaration - III

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Constants may be declared to centralize a value toone location making both readability andmaintenance easier.

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Syntax

Const cPI = 3.

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Note that by convention constants should be alluppercase preceded by a scope identifier.

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Use constants instead of variable when you can.

Declaration - IV

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Scope identifiers^ –

In general there are 3 levels of scope.

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Local (within a routine)

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Object (Covering all routines in an object)

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Global (Covering all routines in all objects)

For local scope it is traditional to use all lowercaseor start with lowercase with an uppercase letter inthe middle:

j,

myTitle

, and

moo

are all good local

variables.

Declaration - VI

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Variables and constants can use up to 30alphanumeric characters A-Z, 0-9, and underbar'_'. Do not use any other punctuation.

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All variables must start with a letter A-Z.

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Declarations are case insensitive. However use ofcase makes your code more readable.

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Some editing tools convert your variables to thedeclared case (e.g., VB, InterDev). By typing all inlowercase, your variables/constants will becorrected to the declared case, helping you toidentify errors in typing more easily.

Declaration - VII

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Since variables are variant type (they can containany value) and functions are usually stronglytyped, it is easy to assign a variable incorrectly, adpass it as an argument. This leads to "involuntarytype conversion“—and errors!

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Dealing with variants IS the #1 source of errors inVBScript.

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VBScript provides a number of conversionfunctions to deal with type issues.