Simple start/stop Javascript timer

timer.js

var Timer = (function Timer() {
  var vars = {
    startTime: 0,
    stopTime: 0,
    time: 0,
    reset: function() {
      vars.startTime = 0;
      vars.stopTime = 0;
      vars.time = 0;
    }
  }
  return function() {
    var _this = this;
    _this.start = function() {
      vars.reset();
      vars.startTime = new Date().getTime();
    };
    _this.stop = function() {
      vars.stopTime = new Date().getTime();
      vars.time = Math.round((vars.stopTime - vars.startTime) / 10);
      return vars.time;
    };
  }
}());