How to open external links in a new tab/window by default?

In order to configure all external links to open in new tabs / windows automatically, i.e. to use the link target "_blank" from an HTML point of view, you have to add some JavaScript to your XWiki:

1. Create a new page, or go to an existing page that won’t be removed
2. Click Edit and select Objects.
3. In the Select a Class box, select JavaScriptExtension and click the Add button.
4. In the object that just appeared, enter the following code into the Code box:
   function fixExternalLinks() {
    var nodes = document.querySelectorAll('.wikiexternallink a');
    for(var i=0; i< nodes.length; i++){
      var link = nodes[i];
      if (link.hasAttribute('target') == false)  {
         link.setAttribute('target', '_blank');
       }
     }
   }
5. Set Use this extension to On this wiki.