title: jquery function val() is not equivalent to "$(this).value="?
body: <p>When I try to set a text input to blank (when clicked) using <code>$(this).value=""</code>, this does not work. I have to use <code>$(this).val('')</code>.</p>
  
  <p>Why? What is the difference? What is the mechanism behind the <code>val</code> function in jQuery?</p>
  
  <pre><code>$(document).ready(function() {
      $('#user_name').focus(function(){
          $(this).val('');
      });
  });
  // error code: not working...
  $(document).ready(function() {
      $('#user_name').focus(function(){
          $(this).value='';
      });
  });
  </code></pre>