@ravi，你的没有调用传入的卸载函数。下面是一个更完整的版本:

/** * Identical to React.useEffect, except that it never runs on mount. This is * the equivalent of the componentDidUpdate lifecycle function. * * @param {function:function} effect - A useEffect effect. * @param {array} [dependencies] - useEffect dependency list. */ export const useEffectExceptOnMount = (effect, dependencies) => { const mounted = React.useRef(false); React.useEffect(() => { if (mounted.current) { const unmount = effect(); return () => unmount && unmount(); } else { mounted.current = true; } }, dependencies); // Reset on unmount for the next mount. React.useEffect(() => { return () => mounted.current = false; }, []); };

我们可以使用useRef钩子来存储我们喜欢的任何可变值，因此我们可以使用它来跟踪useEffect函数是否第一次运行。

如果希望效果与componentDidUpdate运行在同一阶段，可以使用useLayoutEffect代替。

例子

const { useState, useRef, useLayoutEffect } = React; function ComponentDidUpdateFunction() { const [count, setCount] = useState(0); const firstUpdate = useRef(true); useLayoutEffect(() => { if (firstUpdate.current) { firstUpdate.current = false; return; } console.log("componentDidUpdateFunction"); }); return ( <div> <p>componentDidUpdateFunction: {count} times</p> <button onClick={() => { setCount(count + 1); }} > Click Me </button> </div> ); } ReactDOM.render( <ComponentDidUpdateFunction />, document.getElementById("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>

你可以把它变成自定义钩子，像这样:

import React, { useEffect, useRef } from 'react';

const useDidMountEffect = (func, deps) => {
    const didMount = useRef(false);

    useEffect(() => {
        if (didMount.current) func();
        else didMount.current = true;
    }, deps);
}

export default useDidMountEffect;

使用的例子:

import React, { useState, useEffect } from 'react';

import useDidMountEffect from '../path/to/useDidMountEffect';

const MyComponent = (props) => {    
    const [state, setState] = useState({
        key: false
    });    

    useEffect(() => {
        // you know what is this, don't you?
    }, []);

    useDidMountEffect(() => {
        // react please run me if 'key' changes, but not on initial render
    }, [state.key]);    

    return (
        <div>
             ...
        </div>
    );
}
// ...

你可以使用自定义钩子在挂载后运行使用效果。

const useEffectAfterMount = (cb, dependencies) => {
  const mounted = useRef(true);

  useEffect(() => {
    if (!mounted.current) {
      return cb();
    }
    mounted.current = false;
  }, dependencies); // eslint-disable-line react-hooks/exhaustive-deps
};

以下是typescript版本:

const useEffectAfterMount = (cb: EffectCallback, dependencies: DependencyList | undefined) => {
  const mounted = useRef(true);

  useEffect(() => {
    if (!mounted.current) {
      return cb();
    }
    mounted.current = false;
  }, dependencies); // eslint-disable-line react-hooks/exhaustive-deps
};

@ravi，你的没有调用传入的卸载函数。下面是一个更完整的版本:

/** * Identical to React.useEffect, except that it never runs on mount. This is * the equivalent of the componentDidUpdate lifecycle function. * * @param {function:function} effect - A useEffect effect. * @param {array} [dependencies] - useEffect dependency list. */ export const useEffectExceptOnMount = (effect, dependencies) => { const mounted = React.useRef(false); React.useEffect(() => { if (mounted.current) { const unmount = effect(); return () => unmount && unmount(); } else { mounted.current = true; } }, dependencies); // Reset on unmount for the next mount. React.useEffect(() => { return () => mounted.current = false; }, []); };

我做了一个简单的useFirstRender钩子来处理像聚焦表单输入这样的情况:

import { useRef, useEffect } from 'react';

export function useFirstRender() {
  const firstRender = useRef(true);

  useEffect(() => {
    firstRender.current = false;
  }, []);

  return firstRender.current;
}

它开始时为true，然后在useEffect中切换为false，只运行一次，再也不会运行。

在你的组件中使用它:

const firstRender = useFirstRender();
const phoneNumberRef = useRef(null);

useEffect(() => {
  if (firstRender || errors.phoneNumber) {
    phoneNumberRef.current.focus();
  }
}, [firstRender, errors.phoneNumber]);

对于您的情况，只需使用if (!firstRender) {....