<form action="http://cscie12.dce.harvard.edu/echo" method="get">
<h3>How did you hear about us?</h3><p>[<a href="#" id="checkall">check all</a>] [<a href="#" id="uncheckall">uncheck all</a>] [<a href="#" id="togglecheckboxes">toggle</a>]</p>
<ul style="list-style: none;">
<li>
<input type="checkbox" name="how" value="radio"/>Radio</li>
<li>
<input type="checkbox" name="how" value="newspaper"/>Newspaper</li>
<li>
<input type="checkbox" name="how" value="magazine"/>Magazine</li>
<li>
<input type="checkbox" name="how" value="online"/>Online</li>
<li>
<input type="checkbox" name="how" value="friend"/>Friend</li>
</ul>
<input type="submit"/>
</form>
 

In script element within head element (<script type="text/javascript">):

$(document).ready(function() {
  console.log($('#input[name="how"]'));
  $('#checkall').click(function() {
    $('input[name="how"]').prop('checked',true);
    console.log('check all!');
  });
  $('#uncheckall').click(function() {
    $('input[name="how"]').prop('checked',false);
    console.log('uncheck all!');
  });
  $('#togglecheckboxes').click(function() {
    $('input[name=how]').each(function (i) {
      if ($(this).is(':checked')) {
        $(this).prop('checked',false);
      } else {
        $(this).prop('checked',true);
      }     
    });
  });
 });