Missing DIV Tag Causes Web Page to Hang

I am using JavaScript to split test the layout of ads on my web page. Here is part of my web page code:

<script>
      var ads_to_show = "default";
      var random_number = Math.random();

      if (random_number < .5)
      {
        ads_to_show = 1;
      }
      else
      {
        ads_to_show = 2;
      }
    </script>

     <script>
        ad_client = "ca-pub-3412735816916817";
        ad1_display_code = ad2_display_code = ad3_display_code = '<scr' + 'ipt ' + 'src="http://pagead2.googlesyndication.com/pagead/show_ads.js">' + '</scr' + 'ipt>';

        if (ads_to_show == 2)
        {
          ad3_position = "ad_footer_2";
          /* RomanceStuck.com-Footer #2-Content-970x90-Text/Image-Google default-TEST 2 */
          ad3_slot = "4670775136";
          ad3_width = 970;
          ad3_height = 90;
        }
      </script>

      <script>
        google_ad_client = ad_client;
        google_ad_slot = ad3_slot;
        google_ad_width = ad3_width;
        google_ad_height = ad3_height;
        document.write('<div id="' + ad3_position + '" style="width=' + ad3_width + 'px; height=' + ad3_height + 'px;">');
          document.write(ad3_display_code);
        document.write('</div>');
      </script>

The DIV tag with id of "ad_footer_2" only loads if ads_to_show == 2. So, when ads_to_show == 1, that DIV tag doesn't exist but later on in my web page code I still have:

<div id="ad_footer_2_position">
        </div>
        <script>
document.getElementById('ad_footer_2_position').appendChild(document.getElementById('ad_footer_2'));
        </script>

I believe this appendchild code referencing a div that doesn't exist is causing the web page to hang when loading. Is this the cause of the web page hanging and if so, how can I rewrite my code to deal with it.

Thanks!