Jquery ajax validation using remote rule.

The remote rule can be used to validate through ajax call. Field value will be passed through data and the return value to the script that is on url. You can specify data type in dataType that is type of json or text or html.

I used it to check whether username already used or not.

Jquery Code:

$(':input[name="username"]').rules("add",
{
  "remote" :
  {
      url: 'validate_username.php',
      type: "post",
      dataType: "json",
      data:
      {
          username: function()
          {
              return $('#register-form :input[name="username"]').val();
          }
      }
  }
});

PHP script for file validate_username.php

//connect to your db using mysqli

if (!empty($_POST['username']))
{
    $username = $mysqli->real_escape_string($_POST['username']);
    $query = "SELECT ID FROM users WHERE user_name = '{$username}' LIMIT 1;";
    $results = $mysqli->query($query);
    if($results->num_rows == 0)
    {
        echo "true";  //username is not used yet
    }
    else
    {
        echo "false"; //username already used
    }
}
else
{
    echo "false"; //username post variable is not valid.
}