Client-Side Form Field Validation with VBScript and ASP

Form field validation is one of the most important functions in making successful web-based applications, but server-side validation is not always the answer!

Original Author: Glenn Cook

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Client-Side Form Field Validation with VBScript and ASP


Form field validation is one of the most
important functions in making successful web-based applications. It protects
your database from errors, filters bad data, and forces the user to think twice
before submitting data with typos. For some reason though, documentation in many
VBScript and JavaScript books on the market tend to gloss over this issue. I
think it might be that field validation scripting is somewhere between learning
the basics but not complicated enough for the advanced literature. The ASP books
cover server-side validation (Remember? It's a server-side
scripting language.) but this is not always an ideal approach to validating
data. The problems with server-side validation are that it bogs down your server's
resources when the user could handle the routines locally, and it offers a
slower response time for the user when it actually finds errors. This tutorial
is designed to take the load off the servers for a while and get the beginning
weblication programmer closer to the intermediate level and beyond. Have fun!

The goal of the script:

When I click the submit button I want my script
to check the field data in my form and either:


 
  Submit the data if it all looks good
  
Show an alert box and do not send the data.

 


You  need a few tools:


 
  The OnSubmit event.
  
A form name in your HTML code (e.g. <form
   METHOD="POST"
   ACTION="vbsample.asp" name="MyForm">)
  
A Submit Button: (e.g. <input
   TYPE="submit"
   VALUE="Submit Info!"
   name="submit">
  
An Input Box with name: (e.g. <input
   type="text"
   name="MyBox"
   size="10">)
  
Some "If..Then" statements
  
An "Alert Box"
  
The secret. (I love suspense.)

 


Let's see it work before we get into the guts of
it!

 Type your name and submit!
 
Enter nothing and submit!
 
Enter one character and submit!



 
  

  

   

 




 
  
   
    
   
  
  
   
   
  
  
   
   
  
  
   
   
  
  
   
   
  

<SCRIPT
    LANGUAGE="VBScript">
    <-- Option Explicit

    dim validation

    dim header

    header = aspalliance.com

   The
    first thing you want to do is tell the browser that the code you are
    about to run is VBScript.   The next thing you want to do is make
    some variables that we are going to use in our routine.

    The "validation" variable is going to
    be used to help us determine whether we should send the form or not. 
    It will can be equal to either "True" or "False" (By
    the way, that's pretty much the secret ingredient!)

    The "Header" variable I will use to
    hold the string information for a MsgBox property.
Function
    MyForm_OnSubmit
    validation =
    True

   The
    next thing you want to do is make a function that is
    going to be called when a user clicks the "Submit Info"
    button. The function needs to be bound to your form name and the OnSubmit
    event so VB knows what it is that you are trying to submit.  I have
    named my form...."MyForm"

    I have also made my "validation" variable equal to
    "True."   I will follow this with some
    "If...Then" statements that will try to change the variable to
    "False."
If
    Len(Document.MyForm.MyBox.Value) > 2 Then
    MsgBox "You have
    entered too many characters!  You need fewer characters before I
    will submit this form",8, Header

    validation = False

    End If

   My
    first "If...Then" basically says that If the Length
    of the value of the contents of Mybox
    in the form Myform within the current document
    is less than five characters Then show the Message Box(MsgBox).
    The properties of the message box include the message string, then the
    type of message box(8), and I add the header
    message.  The next thing I do is make our validation variable equal
    to False. You'll see why in a second.

    The last thing I do is End this If statement.
If
    (Document.MyForm.MyBox.Value) = "" Then
    MsgBox "You have
    forgotten to fill in the input box!  Why would you want to submit
    nothing in a one field form? C'mon, give me   something to work
    with!",8, Header

    validation = False

    End If

   In
    this "If..Then" I make sure the user has at least entered
    something into the text input box.  If they haven't they will get a
    message box and once again the validation variable will be made equal to
    false.
If
    validation = True Then
    MyForm_OnSubmit =
    True

    Else

    MyForm_OnSubmit =
    False

    End If

    End Function

    </SCRIPT>

   The
    last part of this routine is the secret.

    All I do is test to see if any "If..Then" statement has
    made my validation variable equal to something other than
    "True".  If the validation
    variable equals "True" then MyForm_OnSubmit
    also equals "True."  If the variable
    equals something else other than "True" Then MyForm_OnSubmit
    will equal "False."   If the Function
    equals "False" then the OnSubmit event will not execute and
    the user is prompted to fix their mistake. Otherwise, the OnSubmit event
    fires and the form data is posted to the page that will
    process the submitted form. Simple!
    Finally, End your If,
    tell VBScript to end the Function, and close the script
    with the SCRIPT tag.

   
 


Now granted, this is is a very simple example
and in a real-world application you might have ten to twenty form fields to
validate.   Although there is potential for your script becoming quite
complicated you can use some subroutines that do some work for you. 
Example:

Function MyForm_OnSubmit

Call
Check(Document.MyForm.Company.Value,     "Please enter
a company name.")

Call Check(Document.MyForm.Name.Value,    
"Please enter a name.")

Sub Check(ByVal FieldValue, ByVal
message)

        If FieldValue = "" Then

            MsgBox
message, 8, Header

            validation =
False

            End If

        End Sub

About this post

Posted: 2002-06-01
By: ArchiveBot
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<SCRIPT LANGUAGE="VBScript"> <-- Option Explicit dim validation dim header header = aspalliance.com	The first thing you want to do is tell the browser that the code you are about to run is VBScript. The next thing you want to do is make some variables that we are going to use in our routine. The "validation" variable is going to be used to help us determine whether we should send the form or not. It will can be equal to either "True" or "False" (By the way, that's pretty much the secret ingredient!) The "Header" variable I will use to hold the string information for a MsgBox property.
Function MyForm_OnSubmit validation = True	The next thing you want to do is make a function that is going to be called when a user clicks the "Submit Info" button. The function needs to be bound to your form name and the OnSubmit event so VB knows what it is that you are trying to submit. I have named my form...."MyForm" I have also made my "validation" variable equal to "True." I will follow this with some "If...Then" statements that will try to change the variable to "False."
If Len(Document.MyForm.MyBox.Value) > 2 Then MsgBox "You have entered too many characters! You need fewer characters before I will submit this form",8, Header validation = False End If	My first "If...Then" basically says that If the Length of the value of the contents of Mybox in the form Myform within the current document is less than five characters Then show the Message Box(MsgBox). The properties of the message box include the message string, then the type of message box(8), and I add the header message. The next thing I do is make our validation variable equal to False. You'll see why in a second. The last thing I do is End this If statement.
If (Document.MyForm.MyBox.Value) = "" Then MsgBox "You have forgotten to fill in the input box! Why would you want to submit nothing in a one field form? C'mon, give me something to work with!",8, Header validation = False End If	In this "If..Then" I make sure the user has at least entered something into the text input box. If they haven't they will get a message box and once again the validation variable will be made equal to false.
If validation = True Then MyForm_OnSubmit = True Else MyForm_OnSubmit = False End If End Function </SCRIPT>	The last part of this routine is the secret. All I do is test to see if any "If..Then" statement has made my validation variable equal to something other than "True". If the validation variable equals "True" then MyForm_OnSubmit also equals "True." If the variable equals something else other than "True" Then MyForm_OnSubmit will equal "False." If the Function equals "False" then the OnSubmit event will not execute and the user is prompted to fix their mistake. Otherwise, the OnSubmit event fires and the form data is posted to the page that will process the submitted form. Simple! Finally, End your If, tell VBScript to end the Function, and close the script with the SCRIPT tag.