Javascript事件侦听器

我正在尝试用Javascript做一个简单的Pong游戏。我有一个Pong类，我想创建一种根据鼠标的移动方式来移动播放器矩形的方法：

class Player 
{
  constructor()
  {
   // do stuff
  }
}

class Pong
{
  constructor(canvas)
  {
   //do stuff
   this.player1 = new Player(true); // Create an instance of another class

  }

  handleMouseMove(event)
  {
    var y = event.clientY;

    // this.player1 is undefined!!
    console.log("this.player1: "+this.player1);
    this.player1.pos.y = y;
  }


function main()
{
  // Initialize canvas and context
  canvas = document.getElementById('mycanvas');

  const pong = new Pong(canvas);
  canvas.addEventListener('mousemove', pong.handleMouseMove);
}

每当我开始移动鼠标时，它就会告诉我player1是未定义的。如何将类方法设置为事件侦听器，并使它知道类的成员？