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Warn for bad useEffect return value #14069

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merged 1 commit into from
Nov 2, 2018
Merged

Warn for bad useEffect return value #14069

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22 changes: 20 additions & 2 deletions packages/react-reconciler/src/ReactFiberCommitWork.js
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Original file line number Diff line number Diff line change
Expand Up @@ -295,8 +295,26 @@ function commitHookEffectList(
if ((effect.tag & mountTag) !== NoHookEffect) {
// Mount
const create = effect.create;
const destroy = create();
effect.destroy = typeof destroy === 'function' ? destroy : null;
let destroy = create();
if (typeof destroy !== 'function') {
if (__DEV__) {
if (destroy !== null && destroy !== undefined) {
warningWithoutStack(
false,
'useEffect function must return a cleanup function or ' +
'nothing.%s%s',
typeof destroy.then === 'function'
? ' Promises and useEffect(async () => ...) are not ' +
'supported, but you can call an async function inside an ' +
'effect.'
: '',
getStackByFiberInDevAndProd(finishedWork),
);
}
}
destroy = null;
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In production the branch if (typeof destroy !== 'function') { will still be present with destroy = null. Is it worth keeping it since the next line checks the type again?

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Thanks for the catch, I intended to remove the conditional from the next line.

}
effect.destroy = destroy;
}
effect = effect.next;
} while (effect !== firstEffect);
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28 changes: 28 additions & 0 deletions packages/react-reconciler/src/__tests__/ReactHooks-test.internal.js
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Original file line number Diff line number Diff line change
Expand Up @@ -51,4 +51,32 @@ describe('ReactHooks', () => {
]);
expect(ReactTestRenderer).toHaveYielded(['Did commit: A, B']);
});

it('warns for bad useEffect return values', () => {
const {useLayoutEffect} = React;
function App(props) {
useLayoutEffect(() => {
return props.return;
});
return null;
}
let root;

expect(() => {
root = ReactTestRenderer.create(<App return={17} />);
}).toWarnDev([
'Warning: useEffect function must return a cleanup function or ' +
'nothing.\n' +
' in App (at **)',
]);

expect(() => {
root.update(<App return={Promise.resolve()} />);
}).toWarnDev([
'Warning: useEffect function must return a cleanup function or ' +
'nothing. Promises and useEffect(async () => ...) are not supported, ' +
'but you can call an async function inside an effect.\n' +
' in App (at **)',
]);
});
});