function Test() {

  this.i = 0;

  this.elem = document.getElementById("outtext");

  this.timer = false;

  this.tick = function (){

    this.i++;

    this.elem.value = this.i;

    var self = this;

    this.timer = setTimeout(function(){self.tick();}, 100);

  };

  this.stop = function(){

    if (this.timer) {

      clearTimeout(this.timer);

    }

    this.timer = false;

  };

}

​

var obj = new Test();

​

function start() {

  obj.tick();

}

​

function stop() {

  obj.stop();

}

​