VBScript Tutorial

From http://www.w3schools.com (Copyright Refsnes Data)

VBScript Introduction

What You Should Already Know

Before you continue you should have a basic understanding of the following:

WWW, HTML and the basics of building Web pages

If you want to study these subjects first, go to our Home Page.

What is VBScript?

VBScript is a scripting language

A scripting language is a lightweight programming language

VBScript is a light version of Microsoft's programming language Visual Basic

How Does it Work?

When a VBScript is inserted into a HTML document, the Internet browser will read the HTML and interpret the VBScript. The VBScript can be executed immediately, or at a later event.

VBScript How To ...

How to Put VBScript Code in an HTML Document

<html>

<head>

</head>

<body>

document.write("Hello from VBScript!")

</script>

</body>

</html>

And it produces this output:

Hello from VBScript!

To insert a script in an HTML document, use the <script> tag. Use the type attribute to define the scripting language.

Then comes the VBScript: The command for writing some text on a page is document.write:

document.write("Hello from VBScript!")

The script ends:

</script>

How to Handle Older Browsers

Older browsers that do not support scripts will display the script as page content. To prevent them from doing this, you can use the HTML comment tag:

<!--

some statements

-->

</script>

VBScript Where To ...

Examples

Head section
Scripts can be placed in the head section. Usually we put all the "functions" in the head section. The reason for this is to be sure that the script is loaded before the function is called.

Body section
Execute a script that is placed in the body section. Scripts in the body section are executed when the page is loading.

Where to Put the VBScript

Scripts in a page will be executed immediately while the page loads into the browser. This is not always what we want. Sometimes we want to execute a script when a page loads, other times when a user triggers an event.

Scripts in the head section: Scripts to be executed when they are called or when an event is triggered go in the head section. When you place a script in the head section you will assure that the script is loaded before anyone uses it:

<html>

<head>

some statements

</script>

</head>

Scripts in the body section: Scripts to be executed when the page loads go in the body section. When you place a script in the body section it generates the content of the page:

<html>

<head>

</head>

<body>

some statements

</script>

</body>

Scripts in both the body and the head section: You can place an unlimited number of scripts in your document, so you can have scripts in both the body and the head section.

<html>

<head>

some statements

</script>

</head>

<body>

some statements

</script>

</body>

VBScript Variables

Examples

Create a variable
Variables are used to store information. This example demonstrates how you can create a variable, and assign a value to it.

Insert a variable value in a text
This example demonstrates how you can insert a variable value in a text.

Create an array
Arrays are used to store a series of related data items. This example demonstrates how you can make an array that stores names. ( We are using a "for loop" to demonstrate how you write the names. )

What is a Variable?

A variable is a "container" for information you want to store. A variable's value can change during the script. You can refer to a variable by name to see its value or to change its value. In VBScript, all variables are of type variant, that can store different types of data.

Rules for Variable Names:

Must begin with a letter

Cannot contain a period (.)

Cannot exceed 255 characters

Declaring Variables

You can declare variables with the Dim, Public or the Private statement. Like this:

dim name

name=some value

Now you have created a variable. The name of the variable is "name".

You can also declare variables by using its name in your script. Like this:

name=some value

Now you have also created a variable. The name of the variable is "name".

However, the last method is not a good practice, because you can misspell the variable name later in your script, and that can cause strange results when your script is running. This is because when you misspell for example the "name" variable to "nime" the script will automatically create a new variable called "nime". To prevent your script from doing this you can use the Option Explicit statement. When you use this statement you will have to declare all your variables with the dim, public or private statement. Put the Option Explicit statement on the top of your script. Like this:

option explicit

dim name

name=some value

Assigning Values to Variables

You assign a value to a variable like this:

name="Hege"

i=200

The variable name is on the left side of the expression and the value you want to assign to the variable is on the right. Now the variable "name" has the value "Hege".

Lifetime of Variables

How long a variable exists is its lifetime.

When you declare a variable within a procedure, the variable can only be accessed within that procedure. When the procedure exits, the variable is destroyed. These variables are called local variables. You can have local variables with the same name in different procedures, because each is recognized only by the procedure in which it is declared.

If you declare a variable outside a procedure, all the procedures on your page can access it. The lifetime of these variables starts when they are declared, and ends when the page is closed.

Array Variables

Sometimes you want to assign more than one value to a single variable. Then you can create a variable that can contain a series of values. This is called an array variable. The declaration of an array variable uses parentheses ( ) following the variable name. In the following example, an array containing 3 elements is declared:

dim names(2)

The number shown in the parentheses is 2. We start at zero so this array contains 3 elements. This is a fixed-size array. You assign data to each of the elements of the array like this:

names(0)="Tove"

names(1)="Jani"

names(2)="Stale"

Similarly, the data can be retrieved from any element using the index of the particular array element you want. Like this:

mother=names(0)

You can have up to 60 dimensions in an array. Multiple dimensions are declared by separating the numbers in the parentheses with commas. Here we have a two-dimensional array consisting of 5 rows and 7 columns:

dim table(4, 6)

VBScript Procedures

Examples

Sub procedure
The sub procedure does not return a value.

Function procedure
The function procedure is used if you want to return a value.

VBScript Procedures

We have two kinds of procedures: The Sub procedure and the Function procedure.

A Sub procedure:

is a series of statements, enclosed by the Sub and End Sub statements

can perform actions, but does not return a value

can take arguments that are passed to it by a calling procedure

without arguments, must include an empty set of parentheses ()

Sub mysub()

some statements

End Sub

Sub mysub(argument1,argument2)

some statements

End Sub

A Function procedure:

is a series of statements, enclosed by the Function and End Function statements

can perform actions and can return a value

can take arguments that are passed to it by a calling procedure

without arguments, must include an empty set of parentheses ()

returns a value by assigning a value to its name

Function myfunction()

some statements

myfunction=some value

End Function

Function myfunction(argument1,argument2)

some statements

myfunction=some value

End Function

Call a Sub or Function Procedure

When you call a Function in your code, you do like this:

name = findname()

Here you call a Function called "findname", the Function returns a value that will be stored in the variable "name".

Or, you can do like this:

msgbox "Your name is " & findname()

Here you also call a Function called "findname", the Function returns a value that will be displayed in the message box.

When you call a Sub procedure you can use the Call statement, like this:

Call MyProc(argument)

Or, you can omit the Call statement, like this:

MyProc argument

VBScript Conditional Statements

Examples

The if...then...else statement
This example demonstrates how to write the if...then..else statement.

The if...then...elseif... statement
This example demonstrates how to write the if...then...elseif statement.

The select case statement
This example demonstrates how to write the select case statement.

Conditional Statements

Very often when you write code, you want to perform different actions for different decisions. You can use conditional statements in your code to do this.

In VBScript we have three conditional statements:

if...then...else statement - use this statement if you want to select one of two sets of lines to execute

if...then...elseif statement - use this statement if you want to select one of many sets of lines to execute

select case statement - use this statement if you want to selecct one of many sets of lines to execute

If....Then.....Else

You should use the If...Then...Else statement if you want to

execute some code if a condition is true

select one of two blocks of code to execute

If you want to execute only one statement when a condition is true, you can write the code on one line:

if i=10 Then msgbox "Hello"

There is no ..else.. in this syntax. You just tell the code to perform one action if the condition is true (in this case if i=10).

If you want to execute more than one statement when a condition is true, you must put each statement on separate lines and end the statement with the keyword "End If":

if i=10 Then

msgbox "Hello"

i = i+1

end If

There is no ..else.. in this syntax either. You just tell the code to perform multiple actions if the condition is true.

If you want to execute a statement if a condition is true and execute another statement if the condition is not true, you must add the "Else" keyword:

if i=10 then

msgbox "Hello"

else

msgbox "Goodbye"

end If

The first block of code will be executed if the condition is true, and the other block will be executed otherwise (if i is not equal to 10).

If....Then.....Elseif

You can use the if...then...elseif statement if you want to select one of many blocks of code to execute:

if payment="Cash" then

msgbox "You are going to pay cash!"

elseif payment="Visa" then

msgbox "You are going to pay with visa."

elseif payment="AmEx" then

msgbox "You are going to pay with American Express."

else

msgbox "Unknown method of payment."

end If

Select Case

You can also use the SELECT statement if you want to select one of many blocks of code to execute:

select case payment

case "Cash"

msgbox "You are going to pay cash"

case "Visa"

msgbox "You are going to pay with visa"

case "AmEx"

msgbox "You are going to pay with American Express"

case Else

msgbox "Unknown method of payment"

end select

This is how it works: First we have a single expression (most often a variable), that is evaluated once. The value of the expression is then compared with the values for each Case in the structure. If there is a match, the block of code associated with that Case is executed.

VBScript Looping Statements

Examples

For...next loop
This example demonstrates how to make a simple For....Next loop.

Looping through headers
This example demonstrates how you can loop through the 6 headers in html.

For...each loop
This example demonstrates how to make a simple For.....Each loop.

Do...While loop
This example demonstrates how to make a simple Do...While loop.

Looping Statements

Very often when you write code, you want to allow the same block of code to run a number of times. You can use looping statements in your code to do this.

In VBScript we have four looping statements:

For...Next statement - runs statements a specified number of times.

For Each...Next statement - runs statements for each item in a collection or each element of an array

Do...Loop statement - loops while or until a condition is true

While...Wend statement - Do not use it - use the Do...Loop statement instead

For...Next

You can use a For...Next statement to run a block of code, when you know how many repetitions you want.

You can use a counter variable that increases or decreases with each repetition of the loop, like this:

For i=1 to 10

some code

The For statement specifies the counter variable (i) and its start and end values. The Next statement increases the counter variable (i) by one.

Step Keyword

Using the Step keyword, you can increase or decrease the counter variable by the value you specify.

In the example below, the counter variable (i) is increased by two each time the loop repeats.

For i=2 To 10 Step 2

some code

To decrease the counter variable, you must use a negative Step value. You must specify an end value that is less than the start value.

In the example below, the counter variable (i) is decreased by two each time the loop repeats.

For i=10 To 2 Step -2

some code

Exit a For...Next

You can exit a For...Next statement with the Exit For keyword.

For Each...Next

A For Each...Next loop repeats a block of code for each item in a collection, or for each element of an array.

The For Each...Next statement looks almost identical to the For...Next statement. The difference is that you do not have to specify the number of items you want to loop through.

dim names(2)

names(0)="Tove"

names(1)="Jani"

names(2)="Hege"

For Each x in names

document.write(x & "<br />")

Do...Loop

You can use Do...Loop statements to run a block of code when you do not know how many repetitions you want. The block of code is repeated while a condition is true or until a condition becomes true.

Repeating Code While a Condition is True

You use the While keyword to check a condition in a Do...Loop statement.

Do While i>10

some code

Loop

If i equals 9, the code inside the loop above will never be executed.

some code

Loop While I>10

The code inside this loop will be executed at least one time, even if i is less than 10.

Repeating Code Until a Condition Becomes True

You use the Until keyword to check a condition in a Do...Loop statement.

Do Until i=10

some code

Loop

If i equals 10, the code inside the loop will never be executed.

some code

Loop Until i=10

The code inside this loop will be executed at least one time, even if i is equal to 10.

Exit a Do...Loop

You can exit a Do...Loop statement with the Exit Do keyword.

Do Until i=10

i=i-1

If i<10 Then Exit Do

Loop

The code inside this loop will be executed as long as i is different from 10, and as long as i is greater than 10.