title: JavaScript listen for all focus/blur events
body: <p>So I'd like some JavaScript which listens for all <em>potential</em> focus/blur events on the page. I can do this for click events quite easily:</p>
  
  <pre><code>document.addEventListener('click', function (e) { console.log('click!') })
  </code></pre>
  
  <p>Any time any element is clicked, the event will trigger, even if the node was inserted after the event listener was added.</p>
  
  <p><strong>I'd like to do the same for focus events, but they are only triggered on individual elements, and never bubble up to the document.</strong></p>
  
  <p>How can I accomplish this? Is the only way to walk the DOM every few seconds and re-listen in case a new input element has been added?</p>