我不明白为什么当我使用setTimeout函数时,我的react组件开始到infinite console.log。一切都在工作,但PC开始滞后的地狱。
有人说这个函数在超时时改变我的状态还有那个重新渲染组件,设置新定时器等等。现在我需要知道如何证明它是正确的。
export default function Loading() {
// if data fetching is slow, after 1 sec i will show some loading animation
const [showLoading, setShowLoading] = useState(true)
let timer1 = setTimeout(() => setShowLoading(true), 1000)
console.log('this message will render every second')
return 1
}
明确在不同版本的代码中没有帮助:
const [showLoading, setShowLoading] = useState(true)
let timer1 = setTimeout(() => setShowLoading(true), 1000)
useEffect(
() => {
return () => {
clearTimeout(timer1)
}
},
[showLoading]
)
您的计算机延迟是因为您可能忘记将空数组作为useEffect的第二个参数传递,并在回调中触发了setState。这将导致一个无限循环,因为useEffect在呈现时被触发。
下面是一个在挂载时设置定时器并在卸载时清空定时器的工作方法:
function App() {
React.useEffect(() => {
const timer = window.setInterval(() => {
console.log('1 second has passed');
}, 1000);
return () => { // Return callback to run on unmount.
window.clearInterval(timer);
};
}, []); // Pass in empty array to run useEffect only on mount.
return (
<div>
Timer Example
</div>
);
}
ReactDOM.render(
<div>
<App />
</div>,
document.querySelector("#app")
);
<script src="https://unpkg.com/react@16.7.0-alpha.0/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16.7.0-alpha.0/umd/react-dom.development.js"></script>
<div id="app"></div>
如果你想创建一个类似“start”的按钮,那么使用“useInterval”钩子可能不合适,因为react不允许你调用组件顶部以外的钩子。
export default function Loading() {
// if data fetching is slow, after 1 sec i will show some loading animation
const [showLoading, setShowLoading] = useState(true)
const interval = useRef();
useEffect(() => {
interval.current = () => setShowLoading(true);
}, [showLoading]);
// make a function like "Start"
// const start = setInterval(interval.current(), 1000)
setInterval(() => interval.current(), 1000);
console.log('this message will render every second')
return 1
}
每10秒触发一次api:
useEffect(() => {
const timer = window.setInterval(() => {
// function of api call
}, 1000);
return () => {
window.clearInterval(timer);
}
}, [])
如有状态变化:
useEffect(() => {
// add condition to state if needed
const timer = window.setInterval(() => {
// function of api call
}, 1000);
return () => {
window.clearInterval(timer);
}
}, [state])
您的计算机延迟是因为您可能忘记将空数组作为useEffect的第二个参数传递,并在回调中触发了setState。这将导致一个无限循环,因为useEffect在呈现时被触发。
下面是一个在挂载时设置定时器并在卸载时清空定时器的工作方法:
function App() {
React.useEffect(() => {
const timer = window.setInterval(() => {
console.log('1 second has passed');
}, 1000);
return () => { // Return callback to run on unmount.
window.clearInterval(timer);
};
}, []); // Pass in empty array to run useEffect only on mount.
return (
<div>
Timer Example
</div>
);
}
ReactDOM.render(
<div>
<App />
</div>,
document.querySelector("#app")
);
<script src="https://unpkg.com/react@16.7.0-alpha.0/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16.7.0-alpha.0/umd/react-dom.development.js"></script>
<div id="app"></div>