(this) isn't working; results in “Uncaught TypeError: Cannot read property 'substring' of undefined”

Question

I have the following code which Chrome Inspector debugs with the error "Uncaught TypeError: Cannot read property 'substring' of undefined":

<script type="text/javascript">
  $(function countComments() {
    var mcount = '//api.moot.it/postcounts?path=/forum/comments:' + $(this).closest('article').attr('id').substring(8);
    $.getJSON(mcount, function(json) {
      var results = $('.entry-actions');
      $.each(json, function(key, val) {
        results.prepend('<a class="entry-comments" href="{permalink}#comments" title="Comments">' + val['size'] + ' Comments</a>');
      });
    });
  });
</script>

I'm pretty sure the problem is with (this), but I used it properly in a different script with .click and that code works just fine.

Is it because (this) can't be used on .ready? If so, how could I get this function to work with alternative code?

EDIT with HTML:

<article id="article-5344bff8e4b01730378236ff">
  <header class="entry-header cf">
    <p class="entry-actions"></p>
  </header>
    <div class="entry-title-wrapper">

    BLOG CONTENTS

    <div class="entry-injection">
    <script type="text/javascript">
      $(function countComments() {
        var mcount = '//api.moot.it/postcounts?path=/forum/comments:' + $(this).closest('article').attr('id').substring(8);
        $.getJSON(mcount, function(json) {
          var results = $('.entry-actions');
          $.each(json, function(key, val) {
            results.prepend('<a class="entry-comments" href="{permalink}#comments" title="Comments">' + val['size'] + ' Comments</a>');
          });
        });
      });
    </script>
    </div>
    </div>
  </article>

Answer 1

The problem is that in document ready function this points to document http://jsfiddle.net/IrvinDominin/J2r5V/

In this case you can't have any article parent element of document, so your function raise the error http://jsfiddle.net/IrvinDominin/J2r5V/1/.

I think you have to get all your div elements according on your needs, and for each of them execute the current function; in the context of the each this will be the correct element.