timer that works in web worker

timer.js

var Timer = function() {
  onmessage = this.switchCase.bind(this);
  this.currentTime = 0;
  this.timerId = 0;
};

p = Timer.prototype;

p.switchCase = function(e) {
  switch(e.data) {
    case 0:
      this.stopTimer();
      break;
    case 1:
      this.startTimer();
      break;
    case 2:
      this.getTime();
      break;
  }
};

p.stopTimer = function() {
  clearInterval(this.timerId);
  this.currentTime = 0;
  this.timerId = 0;
  postMessage(0);
};

p.startTimer = function() {
  this.timerId = setInterval(function() {
    this.currentTime++;
  }.bind(this), 1000)
};

p.getTime = function() {
  postMessage(this.currentTime);
};

new Timer();