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Make useEffect(async) warning more verbose #14327

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Merged
merged 2 commits into from
Nov 27, 2018
Merged

Make useEffect(async) warning more verbose #14327

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f9342ac
Make useEffect(async) warning more verbose
gaearon Nov 26, 2018
ea1a9f4
Nit
gaearon Nov 27, 2018
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14 changes: 11 additions & 3 deletions packages/react-reconciler/src/ReactFiberCommitWork.js
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Original file line number Diff line number Diff line change
Expand Up @@ -336,9 +336,17 @@ function commitHookEffectList(
'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.'
? '\n\nIt looks like you wrote useEffect(async () => ...) or returned a Promise. ' +
'Instead, you may write an async function separately ' +
'and then call it from inside the effect:\n\n' +
'async function fetchComment(commentId) {\n' +
' // You can await here\n' +
'}\n\n' +
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More of a question: would it be better to write this function inside the effect callback instead?

Supposedly, the engine would only have to evaluate the function declaration when the effect callback is called, but I'm not sure it'd help anyway as it'd still have to create the shared closure object.

At any rate, writing it outside the component entirely would definitely be better.

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I don't really have an opinion on this but it's nice to show it doesn't have to be inside.

'useEffect(() => {\n' +
' fetchComment(commentId);\n' +
'}, [commentId]);\n\n' +
'In the future, React will provide a more idiomatic solution for data fetching ' +
"that doesn't involve writing effects manually."
: '',
getStackByFiberInDevAndProd(finishedWork),
);
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6 changes: 2 additions & 4 deletions packages/react-reconciler/src/__tests__/ReactHooks-test.internal.js
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Expand Up @@ -75,10 +75,8 @@ describe('ReactHooks', () => {
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 **)',
'Warning: useEffect function must return a cleanup function or nothing.\n\n' +
'It looks like you wrote useEffect(async () => ...) or returned a Promise.',
]);
});

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