// Avoid: Effects with logic that should only ever run once useEffect(() => { loadDataFromLocalStorage(); checkAuthToken(); }, []); // ... } 我想如果前面你认真读过这篇文章,你应该知道问题。前面提到过,在dev环境下,useEffect会触发两次。这可能会导致问题,就以这个代码为例,可能会导致身份验...
importReact,{useEffect}from'react';functionApp(){useEffect(()=>{// Run! Like go get some data from an API.});return({/* Do something with data. */});} In a totally isolated example like that, it’s likely theuseEffectwill run only once. But in a more complex app with props fly...
一些逻辑应该只在应用程序加载时运行一次你可能想将它放在顶层组件的副作用中: function App() {// 🔴 Avoid: Effects with logic that should only ever run onceuseEffect(() => {loadDataFromLocalStorage();checkAuthToken();}, []);// ...} 我想如果前面你有认真读这篇文章,你应该知道问题。前面提到...
useEffect(()=>{console.log("This runs after every render");});useEffect(()=>{console.log("This runs only once, similar to componentDidMount");},[]); 注意事项 不要在循环、条件或嵌套函数中调用useEffect,总是在组件的顶层调用它。 useEffect 返回函数(cleanup function)执行时机 useEffect 的返回函...
useEffect(() => { console.log("This runs after every render"); }); useEffect(() => { console.log("This runs only once, similar to componentDidMount"); }, []); 注意事项不要在循环、条件或嵌套函数中调用 useEffect,总是在组件的顶层调用它。
});useEffect(() =>{console.log("This runs only once, similar to componentDidMount"); }, []); 注意事项 不要在循环、条件或嵌套函数中调用useEffect,总是在组件的顶层调用它。 useEffect 返回函数(cleanup function)执行时机 useEffect 的返回函数被称为“清除函数”(cleanup function)。这个函数的执行时机...
可能在每次渲染时都被重新声明和/或重新赋值）。如果此效果只应执行一次，请使用空依赖项数组：...
When multiple dependencies of a React useEffect() hook change within the same render cycle, its callback will run only once. However, if they change across separate render cycles, then the effect will be triggered separately for each changed dependency. ...
如果某个逻辑必须在每次应用初次加载中运行一次,建议添加一个顶级变量跟踪它是否执行。 letdidInit=false;functionApp(){useEffect(()=>{if(!didInit){didInit=true;// ✅ Only runs once per app loadloadDataFromLocalStorage();checkAuthToken();}},[]);// ...} Event handles 是用户交互事件...
Don’t rush to add Effects to your components. Keep in mind that Effects are typically used to “step out” of your React code and synchronize with some external system. This includes browser APIs, third-party widgets, network, and so on. If your Effect only adjusts some state based on...