Pulse inserted nodes in the DOM

pulse.js

function pulse(node, time) {
  if (!node) throw new Error("node was falsy");

  if (node.constructor && node.constructor == NodeList) {
    var nodes = Array.prototype.slice.call(node);
    nodes.forEach(function (node) { pulse(node, time); });
    return;
  }

  if (!node.style) return;
  if (time === undefined) {
    time = 4000;
  }
  var start = null;
  var original = node.style.backgroundColor;
  function step(timestamp) {
    if (start == null) start = timestamp;
    var progress = timestamp - start;
    if (progress < time) {
      node.style.backgroundColor = "rgba(255, 0, 0, " +  0.5*(1-progress/time) + ")";
      window.requestAnimationFrame(step);
    } else {
      node.style.backgroundColor = original;
    }
  }
  window.requestAnimationFrame(step);
}

if (observer !== undefined) {
  observer.disconnect();
}

var observer = new MutationObserver(function (records) {
  records.forEach(function (record) {
    if (!record.addedNodes) return;
    pulse(record.addedNodes);
  });
});

observer.observe(document.body, { childList: true, subtree: true });