Edit in JSFiddle

class Game {
  constructor(opt) {
    this._canvas = opt.canvas;
    this._ctx = this._canvas.getContext('2d');
    
    this._assets = opt.assets;
    this._loadedAssets = {};
    
    this._fps = opt.fps || 30;
    this._timer;
    this._items = [];
    this._keyboard = '';
    this._setEventListener();
  }
  async start() {
    await this._loadAssets();
    this._timer = setInterval(() => {
      this._render();
    }, 1000 / this._fps);
  }
  stop() {
    clearInterval(this._timer);
  }
  async _loadAssets() {
    const promises = Object.keys(this._assets).map(asset => {
      return new Promise((resolve, reject) => {
        const img = new Image();
        img.onload = () => { resolve(); }
        img.onerror = err => { reject(err); }
        img.src = this._assets[asset];
        this._loadedAssets[asset] = img;
      });
    });

    return Promise.all(promises);
  }
  _render() {
    this._ctx.clearRect(0, 0, this._canvas.clientWidth, this._canvas.clientHeight);
    this._items.forEach(a => {
      a.draw(this._ctx, this._loadedAssets);
      a.update(this._keyboard);
    })
  }
  _setEventListener() {
    window.addEventListener('keydown', e => { this._keyboard = e.key });
    window.addEventListener('keyup', e => { this._keyboard = '' });
  }
  add(item) {
    this._items.push(item);
  }
  remove(item) {
    const idx = this._items.find(a => a === item);
    this._items.splice(idx, 1);
  }
}

class Player {
  constructor(opt = {}) {
    this.x = opt.x || 0;
    this.y = opt.y || 0;
    this.w = opt.w || 64;
    this.h = opt.h || 64;
    this.src = opt.src;
  }
  draw(ctx, assets) {
    if (assets[this.src]) {
      ctx.drawImage(assets[this.src], this.x, this.y, this.w, this.h);
    } else {
      ctx.fillRect(this.x, this.y, this.w, this.h);
    }
  }
  update(keyboard) {
    // ここで動作を定義する
    switch (keyboard) {
      case 'ArrowUp':
        this.y -= 5;
        break;
      case 'ArrowDown':
        this.y += 5;
        break;
      case 'ArrowLeft':
        this.x -= 5;
        break;
      case 'ArrowRight':
        this.x += 5;
        break;
    }
  }
}

function main() {
  const assets = {
    player: 'https://avatars3.githubusercontent.com/u/5305599'
  };
  const game = new Game({
    canvas: document.getElementById('app'),
    assets: assets,
    fps: 30
  });
  
  const player = new Player({
    src: 'player'
  });
  game.add(player);
  
  document.getElementById('start').addEventListener('click', () => game.start());
  document.getElementById('stop').addEventListener('click', () => game.stop());
}
main();

<div>
  <canvas id="app" width="640" height="360"></canvas>
</div>
<button id="start">start</button>
<button id="stop">stop</button>