title: jquery check if value is not null / empty or NaN
body: <p>sI'm currently checking if value is Nan using jQuery and would like to extend the check to not null or empty as well but not sure on how to do this, 
  here's my code;</p>
  
  <pre><code>&lt;script type="text/javascript"&gt; // ensure quantity textbox is numeric
  $(document).ready(function () {
      $('[id$=txtQuantity]').change(function () {
          if(isNaN(this.value)) {
              alert("Please ensure the quantity specified is numeric");
              $(this).val("1");
          }
          else{
              $(this).val(this.value);
          }
      });
  });
  </code></pre>
  
  <p></p>