Element focus utility

I've recently been looking at retrofitting keyboard navigation support to JS Bin, but I was immediately struck by the totally lack of visibility on what was in focus.

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Sure, this is a short-coming of the original design and bad choises I had made with JS Bin's code base. Perhaps you can see from the animation below, when the body is in focus, tabbing is focusing something but until I actually tab to the "HTML" panel title, there's no visual feedback as to what I should be fixing:

If you can see it, the browser's status bar tells me that I'm moving focus, but it's near impossible to work out which element I'm working with.

So I built a mini utility to visualise what's happening. Now with that utility:

Installation

Either add the code directly to your project as a debug dependancy, or use it as a snippet in your devtools:

(function () {
  var active = document.createElement('pre');
  document.body.appendChild(active);
  active.tabindex = -1;
  with (active.style) { // warning: `with` I know what I'm doing!
    position = 'fixed';
    padding = '2px';
    bottom = right = '20px';
    margin = 0;
    fontSize = 12;
    color = '#fff';
    background = '#aaa';
    whiteSpace = 'pre-wrap';
    maxWidth = '95%';
  }

  var lastActive = null;
  var showActive = function () {
    var el = document.activeElement;
    var html = '';
    var attrs = el.attributes;
    var i = 0;

    if (el !== lastActive && el !== active) {
      for (; i < attrs.length; i++) {
        html += ' ' + attrs[i].name + '="' + attrs[i].value + '"';
      }

      active.textContent = '<' + el.nodeName.toLowerCase() + html + '>';
      lastActive = el;
    }

    requestAnimationFrame(showActive);
  };

  showActive();
})();

Here's a live demo:

JS Bin

So now I have visibility on what is being focused, I can fix various issues ranging from outline being removed, only including :hover styles and not :focus and applying proper menu logic to menu-like objects.