jQuery for Designers

Background

Forms are such a common element on the Internet we tend to blunder through them without too much thought. However, if the web site has added a few nice touches that make the process easier, it tends to speed up the process and reduce any frustration in finding our preferred username (i.e. try getting your name under Hotmail!).

There's two types of validation:

1. Simple, server-independent validation, i.e. checking email address are the right format, password and confirm password matches, etc.
2. 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:

1. Only if the value has changed run the check, i.e. ignore meta keys
2. Use a nice ajax spinner to indicate activity
3. 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.

• Full example of username and avatar validation
• Same example with JavaScript removed
• Source code to example