我正在尝试编写自己的可重用 useEffect 挂钩函数useEffectOnce()
以仅运行一次(在挂载和卸载时),但这似乎是不可能的。每次重新渲染后都会调用我的函数:https ://codesandbox.io/s/mjx452lvox
function useEffectOnce() {
console.log("I am in useEffectOnce");
useEffect(() => {
console.log("I am in useEffectOnce's useEffect");
return () => {
console.log("i am leaving useEffectOnce's useEffect");
};
}, []);
}
function App() {
const [count, setCount] = useState(0);
useEffectOnce(); // once!?
return (
<div className="app">
<h3>useEffectOnce (my reusable function)... Wait, once!?</h3>
<button onClick={() => setCount(count + 1)}>
You clicked me {count} times
</button>
</div>
);
}
笔记:
- useEffectOnce() 中的 useEffect() 挂钩按预期工作
useEffectOnce(() => {}, []);
什么都没有改变
...然后大惊喜,与可重复使用的 useState 挂钩函数(!?)的行为相同:https ://codesandbox.io/s/2145m37xnr
useButton
每次重新渲染后都会调用我的函数,并且何时是第一个独立的按钮单击。
function useButton(initialCounterValue) {
const [usebuttoncount, setUseButtonCount] = useState(initialCounterValue);
console.log("I am in useButton");
const handleuseButtonClick = () => {
setUseButtonCount(usebuttoncount + 1);
};
return {
usebuttoncount,
onClick: handleuseButtonClick
};
}
function App() {
const [count, setCount] = useState(0);
const useButtonCounter = useButton(0);
return (
<div className="app">
<h3>
useButton (my reusable useState function) is called only when... OMG!?
</h3>
<button onClick={() => setCount(count + 1)}>
You clicked me {count} times
</button>
<br />
<button {...useButtonCounter}>
(useButton hook) You clicked me {useButtonCounter.usebuttoncount} times
</button>
</div>
);
}