function PlayerTimer() {
    var $this = this;
    this.eventList = {wait:[], play:[]};
    this.timer = null;
    this.interval = 500;
    this.init = function() {
        this.timer = window.setInterval(this.tick, this.interval);
    }
    this.observe = function(event, func) {
          this.eventList[event].push(func);
    }
    this.fire = function (event) {
        for (var i = 0; i < $this.eventList[event].length; $this++) {
            if (!$this.stoped) {
                $this.eventList[event][i]($this);
            }
        }
    }
    this.tick = function() {
        $this.fire('wait');
    }
}

window.playerTimer = new PlayerTimer();
window.playerTimer.observe('play', function() {alert('ok');});

window.playerTimer = new PlayerTimer();
window.playerTimer.init();
window.playerTimer.observe('play', function() {alert('ok');});