Wait for it...

This is an example of a JavaScript solution to Exercise[20].

<!-
The following HTML markup and embedded JavaScript
code has been tested in version 53.0.2785.143 m of
the Chrome web browser and might not work as intended
in other versions of Chrome or in other web browsers.
->

<script>

var popupWindow;

function openPopup() {
  waitForIt(2000);
  popupWindow = window.open("", "", "width=200,height=100");
  popupWindow.document.write("Surprise!");
}

function closePopup() {
  if (popupWindow != undefined) {
    popupWindow.close();
  }
}

/*
 * Timer is a constructor function that may be
 * used to produces instances of objects of 
 * type Timer. An object of type Timer has
 * methods start() and stop() that start
 * and stop a timer, a method called reset
 * that resets a timer, and a method called
 * elaspedTimeInMs that returns an amount of
 * elapsed time. If a timer has been started
 * but not stopped, then elapsedTimeInMs
 * returns the amount of time (in milliseconds)
 * that has elapsed since the timer was started.
 * If a timer has been started and stopped,
 * then elapsedTimeInMs returns the amount of
 * time that elapsed between the time the
 * timer was started and stopped.
 */
function Timer() {
  this.reset();
}
Timer.prototype = {
  reset: function() {
    this.timeStarted = null;
    this.timeStopped = null;
  },
  start: function() {
    this.timeStarted = new Date();
  },
  stop: function() {
    this.timeStopped = new Date();
  },
  elapsedTimeInMs() {
    if (this.timeStarted != null) {
      if (this.timeStopped != null) {
        return this.timeStopped - this.timeStarted;
      }
      else {
        return new Date() - this.timeStarted;
      }
    }
    else {
      return undefined;
    }
  }
};

/*
 * pause does nothing for timeInMs millisends
 * before returning control to the code that
 * called pause. Internally, pause uses a
 * Timer object to wait the specified
 * amount of time before completing.
 */
function pause(timeInMs) {
  // Previously missing code starts here:
  var timer = new Timer();
  timer.start();
  // Previously, missing code ends here.
  while (timer.elapsedTimeInMs() < timeInMs);
}

function waitForIt(delay) {
    alert("Wait for it...");
    pause(delay);
}

</script>

<button onclick="openPopup()">open</button>
<button onclick="closePopup()">close</button>