在带有requestAnimationFrame的Canvas中使用JS倒计时计时器

我正在制作一个简单的画布游戏,我正在使用requestAnimationFrame(PaulIrish的版本)进行游戏循环。我在游戏中使用了javascript倒计时(显示秒和100秒),但它没有以正确的速度倒计时。我知道这与游戏的刷新率有关,所以计数器每帧更新一次,而不是每100秒更新一次。我该如何解决这个问题?

下面是计时器对象:

/**
 * The timer as an object
*/
function Timer(position, time) {
  this.position = position || new Vector(150,210);
  this.time = time || 6000;
}

Timer.prototype = {
  start: function() {
    console.log('start running');
    this.initial = this.time; //time in 100'ths of seconds
    this.count = this.initial;
    this.counter; //10 will  run it every 100th of a second
    clearInterval(this.counter);
    //this.counter = setInterval(this.timer, 10);
    this.timer();
  },

  timer: function() {
    //console.log(this.count);
    this.count--;
      var res = this.count / 100;
    //Show counter in canvas
    return 'Tid kvar: ' + res.toPrecision(this.count.toString().length) + ' sekunder';
  },

  draw: function(ct) {
    if(this.initial === undefined){this.start();} //Start the timer
    ct.save();
    if(this.count <=0){ //Remove timer if timer has reached 0
      ct.clearRect(this.position.x, this.position.y, Racetrack.innerTrackWidth, Racetrack.innerTrackHeight);
      return false;
    } else { //draw timer
      ct.save();
      ct.font = 'bold 3em arial';
      ct.fillStyle = 'orange';
      ct.fillText(this.timer(), this.position.x, this.position.y);
    }
    ct.restore();
  }, 
}

游戏循环和调用计时器的部分:

  var init = function(canvas) {
    timer = new Timer(new Vector(160,210), 3000);
  }

  var render = function() {
    ct.clearRect(0,0,width,height);
    ship.draw(ct);
    racetrack.draw(ct);
    //draw timer or results if timer reached 0
    timer.draw(ct) !=false ? timer.draw(ct) : endFrame.draw(ct);
  };

  var gameLoop = function() {
    var now = Date.now();
    td = (now - (lastGameTick || now)) / 1000; // Timediff since last frame / gametick
    lastGameTick = now;
    if(timer.draw(ct) == false) { //stop the game if timer has reached 0.
      cancelRequestAnimFrame(gameLoop);
      console.log('Time\'s up!');
    } else { //Otherwise, keep the game going.
      requestAnimFrame(gameLoop);
    }
    update(td);
    render();
  };

我也尝试过将其作为计时器对象,但是调试 this.count 显示了第一个循环的编号,未定义第二个循环,之后的每个循环都是NaN(我不确定这会不会解决计时问题?):

function Timer(position, time) {
  this.position = position || new Vector(150,210);
  this.time = time || 6000;
}

Timer.prototype = {
  start: function() {
    console.log('start running');
    this.initial = this.time; //time in 100'ths of seconds
    this.count = this.initial;
    this.counter; //10 will  run it every 100th of a second
    clearInterval(this.counter);
    this.counter = setInterval(this.timer, 10);
    this.timer();
  },


  timer: function() {
    console.log(this.count);
    this.count--;
  },

  getTime: function() {
    var res = this.count / 100;
    return 'Tid kvar: ' + res.toPrecision(this.count.toString().length) + ' sekunder';
  },

  draw: function(ct) {
    if(this.initial === undefined){this.start();} //Start the timer
    ct.save();
    if(this.count <=0){ //Remove timer if timer has reached 0
      ct.clearRect(this.position.x, this.position.y, Racetrack.innerTrackWidth, Racetrack.innerTrackHeight);
      return false;
    } else { //draw timer
      ct.save();
      ct.font = 'bold 3em arial';
      ct.fillStyle = 'orange';
      ct.fillText(this.getTime(), this.position.x, this.position.y);
    }
    ct.restore();
  },
}