game-manager.js

export class GameManager {
  // ...
  restart() {
    // ...
    this.lastUpdate = undefined
    this.stopTime = undefined
  }
  // ...
  tick() {
    if (!this.stopTime) {
      const lastUpdate = Date.now()
      if (this.lastUpdate) {
        this.game.process(lastUpdate - this.lastUpdate, this.controller.movement)
        if (this.game.is_over()) {
          this.restart()
          return
        }
        if (this.game.score > Storage.getBestScore()) {
          localStorage.setItem('bestScore', this.game.score)
          Storage.setBestScore(this.game.score)
        }
      }
      this.lastUpdate = lastUpdate
      this.render()
    }
  }
  // ...
}