Using Ajax to Validate Forms

There’s two types of validation:

Simple, server-independent validation, i.e. checking email address are the right format, password and confirm password matches, etc.
Server-based validation, with can be delivered with a page refresh, or live (as this tutorial will explain), i.e. for checking whether a username is taken.

What can we do?

Live username checking
Password confirmation and strength
Checking if an email address is already registered
URL validation, i.e. Basecamp’s site address checks if the URL is available (pretty much the same as username validation)

So why do it?

It makes the user’s experience quicker, or arguably better
It’s not much extra work to put in place (explained below)

Examples in the wild

Twitter signup / username validation
Pownce signup / username validation (though you have to click ‘check’)
Digg signup / username
Basecamp / URL validation
del.icio.us / tagging

Howto

As with all these tutorials, I expect that you have built your solution to the point where it works, but now we want to add our splash of JavaScript magic.

In our baseline example, my requirements are:

Username validation kept in separate function
Server side does the it’s normal job
I can detect an Ajax request and return something different

Username validation

Our PHP function to validate the username reads:

function check_username($username) {
  $username = trim($username); // strip any white space
  $response = array(); // our response
  
  // if the username is blank
  if (!$username) {
    $response = array(
      'ok' => false, 
      'msg' => "Please specify a username");
      
  // if the username does not match a-z or '.', '-', '_' then it's not valid
  } else if (!preg_match('/^[a-z0-9.-_]+$/', $username)) {
    $response = array(
      'ok' => false, 
      'msg' => "Your username can only contain alphanumerics and period, dash and underscore (.-_)");
      
  // this would live in an external library just to check if the username is taken
  } else if (username_taken($username)) {
    $response = array(
      'ok' => false, 
      'msg' => "The selected username is not available");
      
  // it's all good
  } else {
    $response = array(
      'ok' => true, 
      'msg' => "This username is free");
  }

  return $response;        
}

This format for a response is good, because we are using it to display error messages on the page, but we can also convert it to JSON and use it in our Ajax response later on.

Markup

Again, it’s assumed your markup is already designed to show error messages.

For this example the following markup is being used within a fieldset:

<div>
    <label for="username">Username, valid: a-z.-_</label>
    <input type="text" name="username" value="<?=@$_REQUEST['username']?>" id="username" />
    <span id="validateUsername"><?php if ($error) { echo $error['msg']; } ?></span>
</div>

jQuery

Our client side check will perform the following:

Only if the value has changed run the check, i.e. ignore meta keys
Use a nice ajax spinner to indicate activity
Make an Ajax request and show the response

$(document).ready(function () {
  var validateUsername = $('#validateUsername');
  $('#username').keyup(function () {
    var t = this; 
    if (this.value != this.lastValue) {
      if (this.timer) clearTimeout(this.timer);
      validateUsername.removeClass('error').html('<img src="images/ajax-loader.gif" height="16" width="16" /> checking availability...');
      
      this.timer = setTimeout(function () {
        $.ajax({
          url: 'ajax-validation.php',
          data: 'action=check_username&username=' + t.value,
          dataType: 'json',
          type: 'post',
          success: function (j) {
            validateUsername.html(j.msg);
          }
        });
      }, 200);
      
      this.lastValue = this.value;
    }
  });
});

The code breaks down as follows:

$(document).ready(function () {

Run the JavaScript in this (anonymous) function when the document has loaded.

var validateUsername = $('#validateUsername');

Create a cached copy of the validateUsername span because it will help a little with optimisation (it’s a good practise to have).

$('#username').keyup(function () {

Run the JavaScript in this (anonymous) function on key up.

var t = this;

Cache the ‘this’ instance as we need access to it within a setTimeout, where ‘this’ is set to ‘window’, which can cause all manners of confusion.

if (this.value != this.lastValue) {

Only run the check if the username has actually changed - also means we skip meta keys.

if (this.timer) clearTimeout(this.timer);

The timeout logic means the ajax doesn’t fire with every key press, i.e. if the user holds down a particular key, it will only fire when the release the key.

validateUsername.removeClass('error').html('<img src="images/ajax-loader.gif" height="16" width="16" /> checking availability...');

Show our holding text in the validation message space.

this.timer = setTimeout(function () {

Fire an ajax request in 1/5 of a second.

$.ajax({
  url: 'ajax-validation.php',
  data: 'action=check_username&username=' + t.value,
  dataType: 'json',
  type: 'post',
  success: function (j) {
    validateUsername.html(j.msg);
  }
});

The actual Ajax request. If the script ajax-validation.php returns any response, convert it to JSON and put the ‘msg’ field in to the validation message.

The fields are set in the PHP server response. You can see this working in the demo, and view the source, in particular look at the $resp array from check_username.

this.lastValue = this.value;

Finally, put the current value in to a cache, to make sure we ignore meta keys (from above).

Server response

Now all I have to add to the PHP code, that already handles normal username validation is:

if (@$_REQUEST['action'] == 'check_username' && isset($_SERVER['HTTP_X_REQUESTED_WITH'])) {
    echo json_encode(check_username($_REQUEST['username']));
    exit; // only print out the json version of the response
}

So long as this is high enough in the logic, it will just check the username is valid, using our existing function and convert the response to a JSON object (you may need to add JSON support for PHP, otherwise it’s bundled with PHP 5.2.0).

Example & taking it further

In the example I’ve provided, I’ve also shown how we can add JavaScript to a normally coded page to also validate the user providing an avatar URL.

You should follow me on Twitter here I tweet about jQuery amongst the usual tweet-splurges!

Related screencasts

Ajax Spy Last month I showed you how to create a spy...
Play School: Easy Ajax - load Ajax is made incredibly simple with jQuery. There’s a number...

Demo

If you find this demo doesn't work as expected, it's possibly due to the demo running from within an iframe. Try running the demo in it's own window.

Source Code

Comments

Winten On 28th January 2009 at 15:01

i replaced
```
    } else if (in_array($username, $taken_usernames)) {
```
with my
```
} else if ($username == get(username, $username, NULL)) {
```
and it says ‘checking availability…’ forever, how can i obtain users from sql then?
Azam On 6th April 2009 at 04:04

can we use this script in classic asp?
Harini On 1st July 2009 at 11:07

This is what i was searching for. But how do i use this to check the username availability in the Database?
Marujo On 2nd July 2009 at 14:07

hi. nice work. im using php to post the form in my site. the submit button in the form (contact.html) call a page “send.php” , that send the data, config the email adress to deliver and redirect to ‘ok.html’ page… how can i make this ‘ok’ or ‘error’ in the same page of the form, with ajax/jquery? i dont know so much about programming. can you help me? if you want, i can send my files to you. thanks and continous with great tutos. sorry for my english. im from brazil. thanks!
amir On 7th July 2009 at 17:07

hi, i test your script in my site but not worked

can you tell me what’s your php code?

please see this : http://www.ircloop.com/checkuser.php?action=check_username&username=amir http://www.ircloop.com/indextest.php
MacknonaldS On 8th July 2009 at 01:07

Very informative. A great fundamental background for php and ajax validation. Thanks for this information.
Aqib Mushtaq On 25th July 2009 at 19:07

fantastic tutorial, thanks. i’ve been looking for a tutorial like this one for a long time.
Nix On 8th August 2009 at 20:08

Tnx, mate!!! This is what I was looking for for a long time!! :D Great!
Shoaib Munir On 3rd September 2009 at 10:09

hi

i want to remove check on keyup and i want to add a button for check checking availability like google and yahoo how can i do??
Darryl On 13th September 2009 at 22:09

Do you have a Classic ASP version?
uk On 9th October 2009 at 19:10

This is a very nice tutorial. I used it to write an article about form validation with Ajax in combination with CodeIgniter (as a REST-like API). Thanks for this great howto!
Zul On 27th October 2009 at 23:10

I still don’t know how to connect the array usernames_taken with the database… any idea? how to do it…? I mean, if I want to compare the username inside my db, I got to change it into array too, am i right? so how am i gonna do that?
Bengt On 2nd December 2009 at 16:12

Hello!

Love your article! I’m wondering what I’m doing wrong though, I downloaded your ajax-validation.php and uploaded it to my server. It works, but not with the instantaneous validation. You don’t happen to know what might be wrong?

Thanks in advance!

Cheers, Bengt
Smashing Buzz On 24th March 2010 at 17:03

really helping stuff for web designer and developers, as my experience, me using this in my latest project and helpful for me.