在 useEffect 2nd param 中使用对象而不必将其字符串化为 JSON [英] use object in useEffect 2nd param without having to stringify it to JSON

问题描述

在 JS 中，两个对象不相等.

In JS two objects are not equals.

const a = {}, b = {};
console.log(a === b);

所以我不能在 useEffect(React hooks)中使用一个对象作为第二个参数，因为它总是被认为是 false(所以它会重新渲染):

So I can't use an object in useEffect (React hooks) as a second parameter since it will always be considered as false (so it will re-render):

function MyComponent() {
  // ...
  useEffect(() => {
    // do something
  }, [myObject]) // <- this is the object that can change.
}

这样做(上面的代码)，会导致每次组件重新渲染的运行效果，因为每次都认为对象不相等.

Doing this (code above), results in running effect everytime the component re-render, because object is considered not equal each time.

我可以通过将对象作为 JSON 字符串化值传递来破解"这一点，但 IMO 有点脏:

I can "hack" this by passing the object as a JSON stringified value, but it's a bit dirty IMO:

function MyComponent() {
  // ...
  useEffect(() => {
    // do something
  }, [JSON.stringify(myObject)]) // <- yuck

有没有更好的方法来做到这一点并避免不必要的效果调用?

Is there a better way to do this and avoid unwanted calls of the effect?

旁注:对象具有嵌套属性.效果必须在此对象内的每个更改上运行.

推荐答案

您可以创建一个自定义挂钩来跟踪 ref 中的先前依赖项数组，并将对象与例如Lodash isEqual 并且只运行提供的函数，如果它们不是相等.

You could create a custom hook that keeps track of the previous dependency array in a ref and compares the objects with e.g. Lodash isEqual and only runs the provided function if they are not equal.

示例

const { useState, useEffect, useRef } = React;
const { isEqual } = _;

function useDeepEffect(fn, deps) {
  const isFirst = useRef(true);
  const prevDeps = useRef(deps);

  useEffect(() => {
    const isFirstEffect = isFirst.current;
    const isSame = prevDeps.current.every((obj, index) =>
      isEqual(obj, deps[index])
    );

    isFirst.current = false;
    prevDeps.current = deps;

    if (isFirstEffect || !isSame) {
      return fn();
    }
  }, deps);
}

function App() {
  const [state, setState] = useState({ foo: "foo" });

  useEffect(() => {
    setTimeout(() => setState({ foo: "foo" }), 1000);
    setTimeout(() => setState({ foo: "bar" }), 2000);
  }, []);

  useDeepEffect(() => {
    console.log("State changed!");
  }, [state]);

  return <div>{JSON.stringify(state)}</div>;
}

ReactDOM.render(<App />, document.getElementById("root"));

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js"></script>
<script src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>

<div id="root"></div>

这篇关于在 useEffect 2nd param 中使用对象而不必将其字符串化为 JSON的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！