Demo

Try entering data in the following form and try to submit it with invalid fields.

HTML

<form action="" method="post" id="contact-form">
  <div>
    <label for="name">Name</label>
    <input type="text" name="name" id="name" />
  </div>
  <div>
    <label for="email">E-mail</label>
    <input type="text" name="email" id="email" />
  </div>
  <div>
    <label for="message">Message</label>
    <input type="text" name="message" id="message" />
  </div>
  <div>
    <label for="subject">Subject</label>, select all applicable (use ctrl or cmd to select many)
    <select name="subject" multiple="multiple" size="3">
      <option value="question">Question</option>
      <option value="suggestion">Suggestion</option>
      <option value="bug">Bug</option>
    </select>
  </div>
  <div>
    <input type="submit" value="Send" />
  </div>
</form>

Javascript

$(function() {
  var v = $("#contact-form").jcheck();
  v.validates("name", "message", {presence: true});
  v.validates("email", {format: {"with": "email", message: "is not a valid email"}});
  v.validates("message", {length: {minimum: 20, maximum: 255}});
  v.validates("subject", {length: {minimum: 1, message: "must have a least %{count} select"}});
});

This is just a little taste of what you can do with jCheck, please check the documentation for more examples and explanations of how to do your client side validations with jCheck.