VBScript Introduction
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What You Should Already Know
Before you continue you should have a basic understanding of the following:
- HTML / XHTML
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
- VBScript is only supported by Microsoft's browsers (Internet Explorer)
How Does it Work?
When a VBScript is inserted into an HTML document, Internet Explorer browser will read the HTML and interpret the VBScript. The VBScript can be executed immediately, or at a later event.
VBScript only works in Microsoft browsers (Internet Explorer).
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VBScript How To
The HTML <script> tag is used to insert a VBScript into an HTML page.
Put a VBScript into an HTML Page
The example below shows how to use VBSript to write text on a web page:
Example (IE Only)
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The example below shows how to add HTML tags to the VBScript:
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Example Explained
To insert a VBScript into an HTML page, we use the <script> tag. Inside the <script> tag we use the type attribute to define the scripting language.
So, the <script type="text/vbscript"> and </script> tells where the VBScript starts and ends:
| <html> <body> <script type="text/vbscript"> ... </script> </body> </html> |
The document.write command is a standard VBScript command for writing output to a page.
By entering the document.write command between the <script> and </script> tags, the browser will recognize it as a VBScript command and execute the code line. In this case the browser will write Hello World! to the page:
| <html> <body> <script type="text/vbscript"> document.write("Hello World!") </script> </body> </html> |
How to Handle Simple Browsers
Browsers that do not support scripting, will display VBScript as page content.
To prevent them from doing this, the HTML comment tag should be used to "hide" the VBScript.
Just add an HTML comment tag <!-- before the first VBScript statement, and a --> (end of comment) after the last VBScript statement, like this:
| <html> <body> <script type="text/vbscript"> <!-- document.write("Hello World!") --> </script> </body> </html> |
VBScript Where To ...
VBScripts can be placed in the body and in the head section of an HTML document.
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Where to Put the VBScript
VBScripts 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, or at a later event, such as when a user clicks a button. When this is the case we put the script inside a function or a sub procedure, you will learn about procedures in a later chapter.
Scripts in <head>
Put your functions and sub procedures in the head section, this way they are all in one place, and they do not interfere with page content.
Example (IE Only)
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Scripts in <body>
If you don't want your script to be placed inside a function, and especially if your script should write page content, it should be placed in the body section.
Example (IE Only)
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Scripts in <head> and <body>
You can place an unlimited number of scripts in your document, and you can have scripts in both the body and the head section.
Example (IE Only)
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Using an External VBScript
If you want to run the same VBScript on several pages, without having to write the same script on every page, you can write a VBScript in an external file.
Save the external VBScript file with a .vbs file extension.
Note: The external script cannot contain the <script> tag!
To use the external script, point to the .vbs file in the "src" attribute of the <script> tag:
Example
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Note: Remember to place the script exactly where you normally would write the script!
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VBScript Variables
Variables are "containers" for storing information.
Do You Remember Algebra from School?
Do you remember algebra from school? x=5, y=6, z=x+y
Do you remember that a letter (like x) could be used to hold a value (like 5), and that you could use the information above to calculate the value of z to be 11?
These letters are called variables, and variables can be used to hold values (x=5) or expressions (z=x+y).
VBScript Variables
As with algebra, VBScript variables are used to hold values or expressions.
A variable can have a short name, like x, or a more descriptive name, like carname.
Rules for VBScript variable names:
- Must begin with a letter
- Cannot contain a period (.)
- Cannot exceed 255 characters
In VBScript, all variables are of type variant, that can store different types of data.
Declaring (Creating) VBScript Variables
Creating variables in VBScript is most often referred to as "declaring" variables.
You can declare VBScript variables with the Dim, Public or the Private statement. Like this:
| Dim x Dim carname |
Now you have created two variables. The name of the variables are "x" and "carname".
You can also declare variables by using its name in a script. Like this:
| carname="Volvo" |
Now you have also created a variable. The name of the variable is "carname". However, this 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.
If you misspell for example the "carname" variable to "carnime", the script will automatically create a new variable called "carnime". To prevent your script from doing this, you can use the Option Explicit statement. This statement forces you 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 carname carname=some value |
Assigning Values to Variables
You assign a value to a variable like this:
| carname="Volvo" x=10 |
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 "carname" has the value of "Volvo", and the variable "x" has the value of "10".
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.
VBScript Array Variables
An array variable is used to store multiple values in a single variable.
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) |
Asign data to a two-dimensional array:
Example (IE Only)
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VBScript Procedures
VBScript has two kinds procedures:
- Sub procedure
- Function procedure
VBScript Sub Procedures
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
- without arguments, it must include an empty set of parentheses ()
| Sub mysub() some statements End Sub |
or
| Sub mysub(argument1,argument2) some statements End Sub |
Example (IE Only)
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VBScript Function Procedures
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 |
or
| Function myfunction(argument1,argument2) some statements myfunction=some value End Function |
Example (IE Only)
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How to Call a Procedure
There are different ways to call a procedure. You can call it from within another procedure, on an event, or call it within a script.
Example (IE Only)Call a procedure when the user clicks on a button:
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Procedures can be used to get a variable value:
| carname=findname() |
Here you call a Function called "findname", the Function returns a value that will be stored in the variable "carname".
Function procedures can calculate the sum of two arguments:
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The function "myfunction" will return the sum of argument "a" and argument "b". In this case 14.
When you call a 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
Conditional Statements
Conditional statements are used to perform different actions for different decisions.
In VBScript we have four conditional statements:
- If statement - executes a set of code when a condition is true
- If...Then...Else statement - select one of two sets of lines to execute
- If...Then...ElseIf statement - select one of many sets of lines to execute
- Select Case statement - select one of many sets of lines to execute
If...Then...Else
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 alert("Hello") |
There is no ..Else.. in this syntax. You just tell the code to perform one action if a 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 alert("Hello") i = i+1 End If |
There is no ..Else.. in the example above 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:
Example (IE Only)
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In the example above, the first block of code will be executed if the condition is true, and the other block will be executed otherwise (if i is greater than 10).
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If...Then...ElseIf
You can use the If...Then...ElseIf statement if you want to select one of many blocks of code to execute:
Example (IE Only)
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Select Case
You can also use the "Select Case" statement if you want to select one of many blocks of code to execute:
Example (IE Only)
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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.
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VBScript Looping
Looping Statements
Looping statements are used to run the same block of code a specified number of times.
In VBScript we have four looping statements:
- For...Next statement - runs code a specified number of times
- For Each...Next statement - runs code 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 Loop
Use the For...Next statement to run a block of code a specified number of times.
The For statement specifies the counter variable (i), and its start and end values. The Nextstatement increases the counter variable (i) by one.
Example
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The Step Keyword
With 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 Next |
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 Next |
Exit a For...Next
You can exit a For...Next statement with the Exit For keyword.
| For i=1 To 10 If i=5 Then Exit For some code Next |
For Each...Next Loop
A For Each...Next loop repeats a block of code for each item in a collection, or for each element of an array.
Example
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Do...Loop
If you don't know how many repetitions you want, use a Do...Loop statement.
The Do...Loop statement repeats a block of code while a condition is true, or until a condition becomes true.
Repeat 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.
| Do 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.
Repeat 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.
| Do 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.
