onInterval.js

 _onInterval () {
    const now = Date.now()
    this.setState((oldState) => {
      let { score, level, lastLeft, obstacleIndex } = oldState
      const { right, up, down } = this._controls
      this._resetControls()
      let obstacleSpeed = INITIAL_OBSTACLE_STEP + INITIAL_OBSTACLE_STEP * (0.2) * level
      if (right) {
        obstacleSpeed *= 1 * 6 * Math.min(right, 2)
      }
      let top = oldState.top + FALL_STEP
      if (up) {
        top -= JUMP_STEP * up
      }
      if (down) {
        top += DROP_STEP * down
      }
      
      if (now - this._lastNewObstacles >= NEW_OBSTACLES_TIME) {
        this._lastNewObstacles = now
        const numOfObstacles = oldState.obstacles.length
        if (numOfObstacles) {
          lastLeft = oldState.obstacles[numOfObstacles - 1].left - INITIAL_OBSTACLE_STEP
          if (lastLeft <= INITIAL_LEFT + PLAYER_WIDTH + OBSTACLE_MIN_DISTANCE) {
            lastLeft = INITIAL_LEFT + PLAYER_WIDTH * 3
          }

        } else {
          lastLeft = INITIAL_OBSTACLE_STEP
        }

        for (let i = 0; i < 2; i++) {
          const newObstacle = this._createObstacle(lastLeft, obstacleIndex++, level)
          if (obstacleIndex % OBSTACLES_PER_INDEX === 0) {
            // level++
          }
          lastLeft = newObstacle.left
          oldState.obstacles.push(newObstacle)
        }
      }
      
      if (this._checkIfHit(top)) {
        if (top >= (this._wrapper.offsetHeight - PLAYER_HEIGHT)) {
          top = this._wrapper.offsetHeight - PLAYER_HEIGHT
        } else if (top <= 0) {
          top = 0
        }
        return { ...this._gameOver(), top }
      }
      const obstacles = []
      let hasCollidedWithObstacle = false
      oldState.obstacles.forEach((o) => {
        if (o.left >= OBSTACLE_WIDTH * -1) {
          const newLeft = o.left - obstacleSpeed
          if (INITIAL_LEFT >= (newLeft + OBSTACLE_WIDTH)) {
            o.scored = true
            score += POINTS_PER_OBSTACLE
          }
          if (!hasCollidedWithObstacle) {
            hasCollidedWithObstacle = this._checkColision(INITIAL_LEFT, top, o, newLeft)
          }
          o.left = newLeft
          obstacles.push(o)
        } else if (!o.scored) {
          score += POINTS_PER_OBSTACLE
        }
      })
      if (hasCollidedWithObstacle) {
        return { ...this._gameOver(), top, obstacles, score, obstacleIndex: 0 }
      }
      return { top, obstacles, score, level, lastLeft, obstacleIndex }
    })
  }