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Support sync thenables for lazy() #14626

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merged 2 commits into from Jan 18, 2019
Merged

Support sync thenables for lazy() #14626

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0695c13
Support sync thenables for lazy()
gaearon Jan 18, 2019
7f9f852
Don't commit twice
gaearon Jan 18, 2019
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5 changes: 4 additions & 1 deletion packages/react-reconciler/src/ReactFiberLazyComponent.js
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Expand Up @@ -73,7 +73,10 @@ export function readLazyComponentType<T>(lazyComponent: LazyComponent<T>): T {
}
},
);
lazyComponent._result = thenable;
// Don't race with a sync thenable
if (lazyComponent._status === Pending) {
lazyComponent._result = thenable;
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Alt suggestion:

// Check if it resolved synchronously
if (lazyComponent._status === Resolved) {
  return lazyComponent._result;
}

Since if it's already resolved we don't need to throw the thenable

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Aaaah. That's why it had the loading state. Thanks.

}
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We could also do the same for failure. But doesn't seem worth the extra code to me. Could be a recursive call but then there's more risk of messing it up and going into a stack overflow. Meh.

throw thenable;
}
}
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17 changes: 17 additions & 0 deletions packages/react-reconciler/src/__tests__/ReactLazy-test.internal.js
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Expand Up @@ -61,6 +61,23 @@ describe('ReactLazy', () => {
expect(root).toMatchRenderedOutput('Hi again');
});

it('can resolve synchronously without suspending', async () => {
const LazyText = lazy(() => ({
then(cb) {
cb({default: Text});
},
}));

const root = ReactTestRenderer.create(
<Suspense fallback={<Text text="Loading..." />}>
<LazyText text="Hi" />
</Suspense>,
);

expect(ReactTestRenderer).toHaveYielded(['Loading...', 'Hi']);
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Suggested change
expect(ReactTestRenderer).toHaveYielded(['Loading...', 'Hi']);
expect(ReactTestRenderer).toHaveYielded(['Hi']);

expect(root).toMatchRenderedOutput('Hi');
});

it('multiple lazy components', async () => {
function Foo() {
return <Text text="Foo" />;
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