回答編集履歴
1
追記
test
CHANGED
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@@ -57,3 +57,67 @@
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};
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```
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---
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64
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65
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66
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67
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追記。MyTimer のアンマウント時にタイマーを止めることを考えると useEffect を使うべきでしょうね。
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68
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```js
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const MyTimer = () => {
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75
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const [count, setCount] = useState(0);
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const [timer, setTimer] = useState(false);
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const countup = () => {
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setCount(count => count + 1);
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};
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useEffect(() => {
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if (timer) {
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const timerId = setInterval(countup, 1000);
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return () => clearInterval(timerId);
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}
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}, [timer]);
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return (
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<div>
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<h2>My Timer</h2>
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<div>{String(count)}</div>
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<button onClick={() => setTimer(true)}>スタート</button>
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<button onClick={() => setTimer(false)}>ストップ</button>
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<button onClick={() => setCount(0)}>リセット</button>
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</div>
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);
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};
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```
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