Stuck (once again) on Form Validation


Bow Down to the King
Political User
Here's what I would like to do.

I have a form with the following fields (* = required):

Contact Name (at least 8 characters) *
Company Name
Street Address (at least 8 characters) *
City (at least 5 characters) *
State (select box) *
Zip (5 digits - numbers only) *
Phone (10 characters) *
Fax (10 characters)
Email (check format) *
Message (at least 8 characters) *

To Start
All labels start in black.

Data Input - Valid Data
Label remains black if the data is valid.

Data Input - Invalid Data
Label changes to red if the data is invalid.

If they press submit and all the data is valid then the form transmits. If the data is not valid then an alert will appear.

If anyone knows of a tutorial, a book (available to purchase), or even a tutor/helper (I will pay you for your time) that would guide me in the right direction then please post and let me know.

Thank you.


Bow Down to the King
Political User
Yes, but I don't want to use alert boxes. I am currently using those and I dislike them (annoying at best). I want to learn how to change the text color of the label and use "onChange" or something similar.


I'm sorry Hal...
Political User
well the page was mostly meant to show some validation methods, not just to copy wholesale.

change the event to OnChange (or OnLostFocus)

instead of sending the alert the its something like document.textboxname.className = "failed";

className is a css class, with its text box style set to red or whatever
or set the style property"background-color: red"

(the code is just examples, i haven't looked up exact syntax.
w3schools is a good place to learn


Bow Down to the King
Political User
Okay, I understand so far.

How do I change the style property for a <label>?

I am using <label for="phoneNumber"> ... etc.



OSNN Veteran Addict
I would not recommend changing the label

I typically have this as a form element

<input type="text" name="firstname" id="firstname" size="30"/>

you can then have a javascript on submit which checks the fields, say you have in the validation script a mapping of field ids to validation functions, or maybe a switch case, whatever you choose it doesnt really matter.

If you find an error you can just do
document.getElementById('firstname').className = 'invalid'

If you are using maybe the Prototype javascript library then this can be boiled down to

$('firstname').className = 'invalid'

Also you are going to need to have your validation on the server side as well, so it may well be an idea to just write the validation on the server side then use XmlHttpRequest to validate on the client side using your server side code. Means you only need to have your validation code in one place.


OSNN Veteran Addict
1 vote for ASP.NET 2.0 .. i love me some Visual Studio!
I take it you really like amazingly useless __doPostBack crap that MS decided to use *everywhere*. I wouldn't mind it if it degraded well with Javascript turned off but it doesn't, it just doesnt work at all.


OSNN Senior Addict
I take it you really like amazingly useless __doPostBack crap that MS decided to use *everywhere*. I wouldn't mind it if it degraded well with Javascript turned off but it doesn't, it just doesnt work at all.
I haven't run into any issues - but I could see where it could cause them..


Penguin Rancher
This is a bit brute force, but see if this helps.

<script type="text/javascript">
function validateForm()
 var e;
 // Validate Contact Name
 e = document.getElementById("txtContactName");
 // if bad length, set error 
 if (e.value.length < 8)
  document.getElementById("frmContactErrors").innerHTML = "Contact name must contain 8 characters";
  return;  // exit validation on error
 else // otherwise, clear any old errors
  document.getElementById("frmContactErrors").innerHTML = "";
 // todo: other textbox validation
 // assume if we got this far, there were no errors, so submit
<form name="frmContact" id="frmContact" method="post" action="someurl.php" onsubmit="validateForm();">
<label id="lblContactName" for="txtContactName">Contact Name</label>
<input id="txtContactName" name="txtContactName" type="text" value="" onchange="validateForm();" />
<br />
<label id="lblCompanyName" for="txtCompanyName">Company Name</label>
<input id="txtCompanyName" name="txtCompanyName" type="text" value="" onchange="validateForm();" />
<br />
<input type="button" value="Submit!" onclick="validateForm();" />
<div id="frmContactErrors"><!-- --></div>

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