Not only is it important to use Javascript client side validation it is also important to use server side (ASP) validation as well. Visitors may have Javascript disabled in their browser so it's very important to use server side validation as a backup. Below is the code for a function 'IsValidEmail' that will check the syntax of an email. Note that the function will only check for the proper syntax it will not check to make sure if the email really exists.
<%
'The IsValidEmail function checks for a valid
email
'IsValidEmail returns True if the email address
is a valid email
'IsValidEmail returns false if the email address
isn't proper syntax
'The code is well commented and should explain
what is happening
Function IsValidEmail(emailAddress)
'Declare variables
Dim ValidEmail, emailParts, iLoopCounter, emailChar, acceptableChars, last2Chars
ValidEmail = True 'set the default result to True
'acceptableChars are the characters that we will
allow in our email
acceptableChars="abcdefghijklmnopqrstuvwxyz.-_@"
'use the Split function to create an array with
the @ as the separator
'so if your email was test@tester.com the email
would be split into an array
'with the first array element holding "test"
and the second "tester.com"
emailParts = Split(emailAddress, "@")
'check to make sure that there is only 1 @ and
that there are 2 parts
'remember arrays are zero based
'Using the UBound function will return the highest
element in the array
'So if it's a valid email the UBound function
will return 1, i.e. 0 start
If UBound(emailParts) <> 1 Then
ValidEmail = false
Else
'Check the length of each part of the email address
'first part can be just one character, 2nd part
must be atleast 4
If Len(emailParts(0))<1 OR Len(emailParts(1))<4 Then
ValidEmail = false
End If
'check first character on the left part isn't
a "." using Left function
If Left(emailParts(0), 1)="." Then
ValidEmail = false
End If
'check that there is a . in the second part of
the email address - .com
If InStr(emailParts(1), ".") <= 0 Then
ValidEmail = false
End If
'We know there's a . now make sure there are 2 characters after the . for valid email
last2Chars=Right(emailParts(1),2)
If InStr(last2chars,".") Then
ValidEmail = false
End If
'check that there shouldn't be a _ in the second
part of the email address
If InStr(emailParts(1), "_") >0 Then
ValidEmail = false
End If
End If
'loop through each character of email
For iLoopCounter = 1 to Len(emailAddress)
'Use Lcase & Mid functions, Mid function used
to return each individual character
'in the email, and then Lcase converts it into
lowercase
emailChar = Lcase(Mid(emailAddress, iLoopCounter, 1))
'Check if the emailAddress characters are acceptable
If InStr(acceptableChars, emailChar) = 0 and Not IsNumeric(emailChar)
Then
ValidEmail = false
End if
Next
'check if there is 2 . in a row
If InStr(emailAddress, "..") > 0 Then
ValidEmail=false
End If
'check if there is @. in a row
If InStr(emailAddress, "@.") > 0 Then
ValidEmail=false
End If
IsValidEmail=ValidEmail
End function
%>
Using the function above here are 2 examples:
<% Response.write IsValidEmail("test@testemail") %>
Output:
false
<% Response.write IsValidEmail("test@testemail.com") %>
Output:
True
You may want to read our tutorials on useful VBScript functions and Arrays to help you understand the code better.
Get the best asp web hosting provider now and save 30%
Plug and play ASP membership script that integrates with PayPal to let you charge recurring membership fees.
