When running with bigpipe enabled, back to top repeats

Can confirm that this does fix the issue when big pipe is on.

if ($(context).toArray()[0].constructor.name === 'HTMLDocument')

This looks a little ugly. Why not use the library core/once to ensure backToTop element are added only once ?

Hum you should be able to target multiple elements on the same page. And the syntax looks strange. See https://www.drupal.org/node/3158256 →

var toc_js = $(once('processBackToTop', '.toc-js', context));
toc_js.each(...);

or

var toc_js = once('processBackToTop', '.toc-js', context);
toc_js.forEach(...);

Rewrote to match code example.

Tested with Multiple headings on my page as well as mutliple ToC JS blocks on the same page and can confirm that every heading that was added to the ToC list gets a back to the top. On the headings of the same level in both ToC blocks I do see two links so I can confirm that this is working once for each block.

I did attempt to apply the each to the back to top section

        var opts = $.extend({}, nav.toc.defaults, options);
        if (opts.backToTop) {
          var scrollTo = function(e, callback) {
            if (opts.smoothScrolling && typeof opts.smoothScrolling === 'function') {
              e.preventDefault();
              var elScrollTo = $(e.target).attr('href');

              opts.smoothScrolling(elScrollTo, opts, callback);
            }
            $('li', self).removeClass(opts.activeClass);
            $(e.target).parent().addClass(opts.activeClass);
          };

          nav.find('a').each(function () {
            var container = $(opts.container);
            var anchor = $(this).attr('href').replace(/^#/, '');
            var anchorNameToTop = anchor + '-to-top';
            $(this).attr('id', anchorNameToTop);

            var $span = container.find('span[id="' + anchor + '"]');
            var anchorToTop = $('<a/>')
              .attr('href', '#' + anchorNameToTop)
              .addClass('back-to-top')
              .text(opts.backToTopLabel)
              .insertAfter($span)
              .bind('click', function(e) {
                scrollTo(e, function() {
                });
                nav.trigger('selected', $(this).attr('href'));
              });
          });
        }

but I believe that since this is inside the .each from line 14 it got called mutliple times so the once didn't matter.

Committed. Thanks. For #8 I think it's another issue. If you two block toc-js which target the same heading, then it's normal to have two back-to-top links added. If you wan't limit the number of back-to-top links added, then the question is which anchor choose to only get one back-to-top link. The easier way should be to add a class on the span targeted and then target only the span whitout this class. But it's another issue.

Automatically closed - issue fixed for 2 weeks with no activity.

Is there anything open that prevents releasing this as a stable/supported version? Drupal 9 will soon reach EOL, so a stable release for D10 would be important.