title: jquery validation - optional field
body: <p>In a registration form middleName field is optional. When the users enters his/her middleName, then it should validate that field.</p>
  
  <p>I have used the following code to achieve the above scenario, but it is not working.</p>
  
  <pre><code>$("#middleName").rules("add", {checkName: true, required: false, messages: {checkName: "Please enter a valid middle name"} });
  
  jQuery.validator.addMethod("checkName",
          function(value, element) {
              var regExp = new RegExp(/^[a-zA-Z0-9\s|\,|\.|\-|\']+$/);
              return regExp.test(value);
          },
          "Please enter a valid name."
  );
  </code></pre>
  
  <p>Can anyone suggest me to achieve the above scenario.</p>