JSFiddle - React, Tailwind, and code Playground

HTML

<a href=":8080/test/blah">Test absolute</a>
<a href=":7051./test/blah">Test relative</a>

JavaScript

// delegate event for performance, and save attaching a million events to each anchor
    document.addEventListener('click', function(event) {
      var target = event.target;
      if (target.tagName.toLowerCase() == 'a')
      {
          var port = target.getAttribute('href').match(/^:(\d+)(.*)/);
          if (port)
          {
             target.href = port[2];
             target.port = port[1];
          }
      }
    }, false);