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Resolve the .default export of a React.lazy as the canonical value #34906

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Merged
merged 3 commits into from
Oct 19, 2025
Merged

Resolve the .default export of a React.lazy as the canonical value #34906

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77736db
Resolve the .default export of a React.lazy as the canonical value
sebmarkbage Oct 18, 2025
dabb590
Hide unhandled rejections
sebmarkbage Oct 18, 2025
a12cc9a
Gate on enableAsyncDebugInfo
sebmarkbage Oct 19, 2025
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31 changes: 27 additions & 4 deletions packages/react/src/ReactLazy.js
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,8 @@ import {enableAsyncDebugInfo} from 'shared/ReactFeatureFlags';

import {REACT_LAZY_TYPE} from 'shared/ReactSymbols';

import noop from 'shared/noop';

const Uninitialized = -1;
const Pending = 0;
const Resolved = 1;
Expand Down Expand Up @@ -67,12 +69,20 @@ export type LazyComponent<T, P> = {

function lazyInitializer<T>(payload: Payload<T>): T {
if (payload._status === Uninitialized) {
let resolveDebugValue: (void | T) => void = (null: any);
let rejectDebugValue: mixed => void = (null: any);
if (__DEV__ && enableAsyncDebugInfo) {
const ioInfo = payload._ioInfo;
if (ioInfo != null) {
// Mark when we first kicked off the lazy request.
// $FlowFixMe[cannot-write]
ioInfo.start = ioInfo.end = performance.now();
// Stash a Promise for introspection of the value later.
// $FlowFixMe[cannot-write]
ioInfo.value = new Promise((resolve, reject) => {
resolveDebugValue = resolve;
rejectDebugValue = reject;
});
}
}
const ctor = payload._result;
Expand All @@ -92,12 +102,20 @@ function lazyInitializer<T>(payload: Payload<T>): T {
const resolved: ResolvedPayload<T> = (payload: any);
resolved._status = Resolved;
resolved._result = moduleObject;
if (__DEV__) {
if (__DEV__ && enableAsyncDebugInfo) {
const ioInfo = payload._ioInfo;
if (ioInfo != null) {
// Mark the end time of when we resolved.
// $FlowFixMe[cannot-write]
ioInfo.end = performance.now();
// Surface the default export as the resolved "value" for debug purposes.
const debugValue =
moduleObject == null ? undefined : moduleObject.default;
resolveDebugValue(debugValue);
// $FlowFixMe
ioInfo.value.status = 'fulfilled';
// $FlowFixMe
ioInfo.value.value = debugValue;
Comment on lines +111 to +118
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@eps1lon eps1lon Oct 19, 2025

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This block isn't gated on enableAsyncDebugInfo but resolveDebugValue is only callable with enableAsyncDebugInfo. enableAsyncDebugInfo isn't enabled everywhere at the moment.

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@eps1lon eps1lon Oct 19, 2025

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I guess this is implied via payload._ioInfo but still nice for DCE and readability to gate it.

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@sebmarkbage sebmarkbage Oct 19, 2025

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Fixed. The whole block should've been gated before just like the reject.

}
// Make the thenable introspectable
if (thenable.status === undefined) {
Expand All @@ -124,6 +142,14 @@ function lazyInitializer<T>(payload: Payload<T>): T {
// Mark the end time of when we rejected.
// $FlowFixMe[cannot-write]
ioInfo.end = performance.now();
// Hide unhandled rejections.
// $FlowFixMe
ioInfo.value.then(noop, noop);
rejectDebugValue(error);
// $FlowFixMe
ioInfo.value.status = 'rejected';
// $FlowFixMe
ioInfo.value.reason = error;
}
// Make the thenable introspectable
if (thenable.status === undefined) {
Expand All @@ -139,9 +165,6 @@ function lazyInitializer<T>(payload: Payload<T>): T {
if (__DEV__ && enableAsyncDebugInfo) {
const ioInfo = payload._ioInfo;
if (ioInfo != null) {
// Stash the thenable for introspection of the value later.
// $FlowFixMe[cannot-write]
ioInfo.value = thenable;
const displayName = thenable.displayName;
if (typeof displayName === 'string') {
// $FlowFixMe[cannot-write]
Expand Down
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