systemWakeupWorker.js

var myWorker = new Worker("DetectWakeup.js");
myWorker.onmessage = function (ev) {
  if (ev && ev.data === 'wakeup') {
     // wakeup here
  }
}

// DetectWakeup.js (put in a separate file)
var lastTime = (new Date()).getTime();
var checkInterval = 10000;

setInterval(function () {
    var currentTime = (new Date()).getTime();

    if (currentTime > (lastTime + checkInterval * 2)) {  // ignore small delays
        postMessage("wakeup");
    }

    lastTime = currentTime;
}, checkInterval);