title: TypeError: a is undefined
body: <p>I get the above error on the jQuery v1.7.2 code when I try to use the <code>$.each</code> method:</p>
  
  <pre><code>$.post('url_of_php_file.php',
              $.param( {
  
              }),
              function(data){
                  $.each(data.articles, function(index, value){
                  .....
  });
  </code></pre>
  
  <p>The request returns:</p>
  
  <pre><code>{"articles": [
      {
          "id":"11",
          "date":"2012-12-19 15:52:06",
          "title":"url_title",
          "link":"url_link",
          "available":"1"
       },
      ..... *more rows like the above*
  ]}
  </code></pre>
  
  <p>Why do I get this error?</p>