Load Disqus comments only on demand if you give a shit about page weight and your visitors. Even with no comments, i.e. an empty comment form, calling Disqus will load an extra 226Kb. If your page has comments this can be far higher. This Gist accompanies my blog post: http://internet-inspired.com/wrote/load-disqus-on-demand/

gistfile1.js

// Requires jQuery of course.
$(document).ready(function() {
    $('.show-comments').on('click', function(){
          var disqus_shortname = 'YOUR-DISQUS-USERNAME'; // Replace this value with *your* username.

          // ajax request to load the disqus javascript
          $.ajax({
                  type: "GET",
                  url: "http://" + disqus_shortname + ".disqus.com/embed.js",
                  dataType: "script",
                  cache: true
          });
          // hide the button once comments load
          $(this).fadeOut();
    });
});

gistfile2.html

<!-- An element a visitor can click if they <3 comments! -->
<button class="show-comments">Load Disqus comments</button>

<!-- The empty element required for Disqus to loads comments into -->  
<div id="disqus_thread"></div>

Fixed: I fixed the problem. The problem was that blogger redirects to the country specific blogger domain. That's when disqus looses the thread-url. I needed to use the disqus variables from their original code (https://help.disqus.com/customer/portal/articles/888340-manually-adding-a-disqus-gadget-to-blogger). The second problem was the embed.js script. I changed it to blogger_item.js and now everything works fine.

(original question)
When I use this code for my blog, commens which already have been postet to it are not displayed. Somehow Disqus can not make the reference to the previous comments. Is there a way to fix this? Can I use the page URL as parameter somehow? I created a test-blog and there it works. Only difference: my shortname. the shortname for my real blog has "-" in it. Can it effect it? Do I need to escape them?

It's more practical to use protocol-relative URL, '//' instead of 'http://'. Disqus also suggests it in their template code.

How does this work on WordPress blog posts?

@seb86 you could just place the HTML code into the single.php file and the SCRIPT into the footer.php and that should do it.

@rrecinos Do I not have to specify a post ID?

Possible to make that button toggle comments on and off?

Thank you very much 👍

Piggybacking off of euler0's comment, in this day and age you really just want to use HTTPS instead of protocol-relative.

See for example https://jeremywagner.me/blog/stop-using-the-protocol-relative-url

Why does it has to be jquery? Can't JavaScript do this? Since it's to reduce bloat might as well do it in pure JavaScript.

How to specifiy postID etc... ?