A note about not firing side effects in useState(prev => next) ?

So I ended up doing this by mistake after a wonky merge:

let Foo = (props) => {
    let [bar, setBar] = useState();
    
    let handleClick = () => {
        useState(bar => {
            let newBar = bar + 1;
            props.handleBarChange(newBar); // bad, which isn't surprising
            return newBar;
        });
    };

    return <div onClick={handleClick}>click me</div>;
};

If you fire a side effect such as calling something that sets state in a higher component from a useState updater function, you get the error "Cannot update a component from inside the function body of a different component" (but not always! It seems to depend on internal timing). This definitely seems like a bad idea when you look at it, but I couldn't find any mention in the docs that this is bad.

https://reactjs.org/docs/hooks-reference.html#functional-updates

There is the note about side effects generally on useEffect:

Mutations, subscriptions, timers, logging, and other side effects are not allowed inside the main body of a function component (referred to as React’s render phase)

But this is not in the main body of a function component, doesn't feel like a true side effect as it's still just setting state within React, and doesn't feel like it's in the render phase either.

I initially wanted to comment about this here (https://github.com/facebook/react/issues/18178), because the general message of that thread was "don't set state of another component in a render method", and I've managed to get this error message without doing that, but the thread is locked. Thanks.

從連結的 Hooks 參考頁面開始，尤其是函式式更新部分，並將其中的指引與引用的關於 useEffect 副作用的註記進行比較。釐清 useState updater 中的副作用是否不受支援，並說明相關行為；當文件能夠毫無歧義地處理這個範例時，即視為完成。