useEffect dependency array and ESLint exhaustive-deps rule

问题

I have a component that looks like this:

const MyComponent = props => {
  const { checked, onChange, id } = props;
  const [isChecked, setChecked] = useState(false);

  useEffect(() => {
    onChange && onChange({ isChecked: !!checked, id });
    setChecked(checked);
  }, [checked]);

  const childProps = {
    id,
    isChecked
  };

  return <ChildComponent {...childProps} />;
};

The exhaustive-deps lint rule isn't happy:

React Hook useEffect has missing dependencies: id and onChange. Either include them or remove the dependency array. (react-hooks/exhaustive-deps)eslint

I know that id and onChange are not going to change, so adding them to the dependency array seems unnecessary. But the rule isn't a warning, it's a clear instruction to do something.

Is the ESLint rule:

1) Over-cautious and a bit dumb in this instance, so safe to ignore?

2) Highlighting best practice - i.e. to minimise unexpected bugs that might occur in future if, for instance, changes in parent components mean that id will change at some point in future?

3) Showing an actual/possible problem with the code as it currently is?

回答1:

Actually the rule is very straightforward: Either pass an array containing all dependencies, or don't pass anything. So I guess the rule isn't dumb, it just doesn't know if the dependencies are going to change or not. So yes, if you are passing an array of dependencies it should contains ALL dependencies, including those you know for a fact that will not change. Something like this will throw a warning:

useEffect(() => dispatch({someAction}), [])

And to fix this you should pass dispatch as a dependency, even though it will never change:

useEffect(() => dispatch({someAction}), [dispatch])

Don't disable the exhaustive deps rule, as mentioned here

回答2:

The way to look at it is every render has its own effect. If the effect will be the same with a particular set of values, then we can tell React about those values in the dependencies array. Ideally, a component with the same state and props, will always have the same output (rendered component + effect) after its render and effect is done. This is what makes it more resilient to bugs.

The point of the rule is that, if the deps DO change, the effect SHOULD run again, because it is now a different effect.

These 3 links also give more insights about this:

https://github.com/facebook/react/issues/14920#issuecomment-471070149
https://overreacted.io/a-complete-guide-to-useeffect/
https://overreacted.io/writing-resilient-components/

来源：https://stackoverflow.com/questions/56972415/useeffect-dependency-array-and-eslint-exhaustive-deps-rule

标签

reactjs

react-hooks

use-effect