title: Disabling submit button until multiple checkboxes are checked
body: <p>I would like to disable a form submit button until 4 checkboxes are checked. I created a quick <a href="http://jsfiddle.net/CPFns/47" rel="nofollow">jsfiddle</a> to represent my code that is not working as expected.  </p>
  
  <p>Here is my JS:</p>
  
  <pre><code>$(function() {
    $("#question1, #question2, #question3, #question4").change(function() {
      if( $("#question1").checked &amp;&amp; $("#question2").checked &amp;&amp; $("#question3").checked &amp;&amp;       $("#question4").checked ) {
        $('.next_button').disabled = false; 
      }
      else {
        $('.next_button').disabled = true;
      }
    });
  });
  </code></pre>
  
  <p>And the HTML:</p>
  
  <pre><code>&lt;input id="question1" name="question1" type="checkbox" value="1"&gt;
  &lt;input id="question2" name="question2" type="checkbox" value="1"&gt;
  &lt;input id="question3" name="question3" type="checkbox" value="1"&gt;
  &lt;input id="question4" name="question4" type="checkbox" value="1"&gt;
  &lt;input class="next_button" name="commit" type="submit" value="Next" disabled=""&gt;
  </code></pre>
  
  <p>I am missing something simple here.  Appreciate any thoughts! </p>