Link to test case:

Difficult to provide as DataTables debugger does not work on a custom element, with a shadow-root. See below.

Debugger code (debug.datatables.net):

     function outerHTML(node) {
         // if IE, Chrome take the internal method otherwise build one
         return node.outerHTML || (function (n) {
             if (n === document) {
                 return "";
             }
             var div = document.createElement('div'), h;
             div.appendChild(n.cloneNode(true));            <<<<<< This line fails
             h = div.innerHTML;
             div = null;
             return h;
         })(node);
     }

Error messages shown:

Browser console shows:

Uncaught NotSupportedError: Failed to execute 'cloneNode' on 'Node': ShadowRoot nodes are not clonable.

Description of problem:

I'm unable to create a test case for my actual problem because the shown function in the debugger breaks on the call to cloneNode.

I tried to override the file in the browser, and edit the code to return a few lines earlier (at if (n === document) but that breaks later with a JSON parse error "alert" dialog.