index.js

class Snake {
  ...
  update() {
    ...
    this._previousTailPosition = Object.assign({}, this.parts[this.parts.length - 1]);
    this.parts[this.parts.length - 1] = next;
    const lastPart = this.parts.splice(-1, 1)[0];
    this.parts.unshift(lastPart);

    updates.push({ point: this.head, state: 'on' });
    updates.push({ point: this._previousTailPosition, state: 'off' });
    return updates;
  }

  get previousTailPosition() {
    return this._previousTailPosition;
  }

  grow() {
    this.parts.push(Object.assign({},this.previousTailPosition));
    return { point:this.previousTailPosition, state:'on' };
  }
}

class Game {
  ...
  async run() {
    ...
    while (true) {
      ...
      if(this.food) {
        if(!this.food.isRendered) {
          grid.setPoint(this.food, 'food');
          this.food.isRendered = false;
        }
        if(this.snake.collision(this.snake.head, this.food)) {
          const growUpdate = this.snake.grow();
          this.grid.setPoint(growUpdate.point, growUpdate.state);
          this.food = null;
        }
      }
      ...
    }
  }
}