How to obtain URL from a rel=canonical tag using Javascript

I’m using Disqus comments system and I’m trying to use the feature of adding comment count links.

The code that I can use is below:

<span class="disqus-comment-count" data-disqus-url="http://example.com/article1.html">Comments</span>

And this is where I have some issue. The thing is I have several hundreds of pages so editing the data-disqus-url value for each and every html pages will take a very long time and not feasible. Is there maybe some Javascript code that will dynamically input the data-disqus-url value with my canonical url?

I can’t use php code since I’m using html files but I have SSI enabled since I need to use includes for easy template management. Also, all my html pages already have a unique meta tag for rel=”canonical”. I just need perhaps some Javascript codes that will fill-up the data-disqus-url value with the value indicated in my canonical url tag. Is that possible?