function Timer(callback, delay) {
  var timerId, start, remaining = delay;

  this.pause = function() {
    clearTimeout(timerId);
    remaining -= new Date() - start;
  };

  this.resume = function() {
    start = new Date();
    clearTimeout(timerId);
    timerId = setTimeout(callback, remaining);
  };

  this.getElapsedTime = function() {
    return new Date() - start;
  };

  this.clear = function() {
    clearTimeout(timerId);
  };

  this.resume();
}