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A Complete Example of Form Validation with the DOM


If you’re one of those web developers who want to learn a straightforward and comprehensive method for validating online forms with the DOM, then I have good news for you. Welcome to the second installment of the series “Form validation with the DOM.” This three-part series walks you through taking advantage of the already popular Document Object Model to check user-supplied data by utilizing its handy methods and your own client-side verification routines.

Author Info:
By: Alejandro Gervasio
Rating: 5 stars5 stars5 stars5 stars5 stars / 23
October 31, 2006
TABLE OF CONTENTS:
  1. · A Complete Example of Form Validation with the DOM
  2. · Refreshing some basic concepts
  3. · Improving the program's look and feel
  4. · Styling the sample form and the error messages
  5. · Putting the pieces together

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A Complete Example of Form Validation with the DOM - Putting the pieces together
(Page 5 of 5 )

As I expressed in the section that you just read, I'm certain that you want to see how the complete source code of this DOM-based form validation application looks. Thus, attending to this specific requirement, below I listed the entire form data checking script, together with the pertinent set of CSS rules:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> <title>DOM-based form validator</title> <script language="javascript"> // validate form function validateForm(formObj){             valid=true;             var fname=formObj.elements[0];             if(!fname){return};             if(!fname.value){showError(fname,'Enter your First Name')};             var lname=formObj.elements[1];             if(!lname){return};             if(!lname.value){showError(lname,'Enter your Last Name')};             var email=formObj.elements[2];             if(!email){return};             if(!email.value){showError(email,'Enter your email address')};             var age=formObj.elements[3];             if(!age){return};             if(!age.value){showError(age,'Enter your age (1-99)')};             var postadd=formObj.elements[4];             if(!postadd){return};             if(!postadd.value){showError(postadd,'Enter your postal
address')};             return valid; } // display error messages function showError(obj,message){             if(!obj.errorNode){                         obj.onchange=hideError;                         var span=document.createElement('span');                         span.className='error';                         span.appendChild(document.createTextNode(message));                         obj.parentNode.appendChild(span);                         obj.errorNode=span;             }             valid=false;             return } // hide error messages function hideError(){             this.parentNode.removeChild(this.errorNode);             this.errorNode=null;             this.onchange=null; } // execute 'ValidateForm()' function when page is loaded window.onload=function(){             // check if browser is W3CDOM compatible             if(document.getElementById&&document.
getElementsByTagName&&document.createElement){                         var theform=document.getElementsByTagName
('form')[0];                         if(theform){theform.onsubmit=function()
{return validateForm(this)}};     } } </script> <style type="text/css"> body{             margin: 0;             padding: 0;             background: #fff; } #formcontainer{             width: 600px;             height: 450px;             background: #eee;             margin-left: auto;             margin-right: auto;             border: 1px solid #ccc; } #labelcontainer{             float: left;             width: 200px;             text-align: right;             padding-right: 10px; } #labelcontainer p{             font: normal 12px Arial, Helvetica, sans-serif;             color: #000;             margin: 10px 0 0 0; } #boxcontainer{             float: left;             width: 300px; } #boxcontainer p{             font: normal 12px Arial, Helvetica, sans-serif;             color: #000;             margin: 4px 0 0 0; } span{             font: bold 12px Arial, Helvetica, sans-serif;             color: #f00;             margin-left: 10px; } </style> </head> <body> <div id="formcontainer"> <form action="processform.php" method="post"> <div id="labelcontainer"> <p>First Name</p> <p>Last Name</p> <p>Email</p> <p>Age</p> <p>Postal Address</p> <p>Comments</p> </div> <div id="boxcontainer"> <p><input type="text" name="fname" /></p> <p><input type="text" name="lname" /></p> <p><input type="text" name="email" /></p> <p><input type="text" name="age" /></p> <p><input type="text" name="paddress" /></p> <p><textarea rows="10" cols="20"></textarea></p> <p><input type="submit" name="send" value="Send Data" /></p> </div> </form> </div> </body> </html>

That's about it. Of course, feel free to replace the existing JavaScript validation functions with yours, so you can fine tune the previous script. Hopefully, you'll end up with a fully-functional form checking application that uses the DOM for manipulating dynamically the tree of the respective web document.

Final thoughts

In this second part of the series, I demonstrated how to improve the overall look and feel of this DOM-driven form validation application by including some comprehensive CSS declarations into the original script.

However, you'll enjoy the best of the fruit only in the final tutorial, since in that article I'll show you how to integrate this client-side script will a full-featured form validation class created with PHP 5. You don't have any excuses to miss it!


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