componentDidUpdate.js

class App extends Component {
    state = {...};
    runStopButton = () => {...}
    handleClearBoard = () => {...}
    handleNewBoard = () => {...}
    handleToggleCellStatus = () => {...}
    handleStep = () => {...}
                        
    handleSpeedChange = newSpeed => {
        this.setState({ speed: newSpeed });
    }

    handleRun = () => {
        this.setState({ isGameRunning: true });
    }

    handleStop = () => {
        this.setState({ isGameRunning: false });
    }

    componentDidUpdate(prevProps, prevState) {
        const { isGameRunning, speed } = this.state;
        const speedChanged = prevState.speed !== speed;
        const gameStarted = !prevState.isGameRunning && isGameRunning;
        const gameStopped = prevState.isGameRunning && !isGameRunning;

        if ((isGameRunning && speedChanged) || gameStopped) {
            clearInterval(this.timerID);
        }

        if ((isGameRunning && speedChanged) || gameStarted) {
            this.timerID = setInterval(() => {
                this.handleStep();
            }, speed);
        }
    }
                        
    // Render method ...
}