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feat: Thenable utility #15

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feat: Thenable utility #15

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335591a
Update core.ts
lxsmnsyc Jan 13, 2025
f0f7f36
Update core.ts
lxsmnsyc Jan 14, 2025
44aeebe
Update core.ts
lxsmnsyc Jan 14, 2025
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49 changes: 49 additions & 0 deletions src/core.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@ import type {
FiberRoot,
MemoizedState,
ReactRenderer,
Thenable,
} from './types.js';

// https://github.com/facebook/react/blob/main/packages/react-reconciler/src/ReactWorkTags.js
Expand Down Expand Up @@ -261,6 +262,54 @@ export const traverseProps = (
return false;
};

export type ThenableData =
| ({ status: 'fulfilled'; value: unknown } & Thenable<unknown>)
| ({ status: 'rejected'; reason: unknown } & Thenable<unknown>)
| ({ status: 'pending' } & Thenable<unknown>);

interface ThenableState {
_debugThenableState: ThenableData[] | { thenables: ThenableData[] };
}

function isThenableState(dependencies: object): dependencies is ThenableState {
return '_debugThenableState' in dependencies;
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is this available in the react production build?

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@lxsmnsyc lxsmnsyc Jan 17, 2025 •
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Yeah it's dev-only, had to check first if it's assigned.

}

export const getThenables = (fiber: Fiber): ThenableData[] => {
if (fiber.dependencies && isThenableState(fiber.dependencies)) {
// https://github.com/facebook/react/blob/b3a95caf61bc716fb618997e6e9f3a0c8c9c8374/packages/react-reconciler/src/ReactFiberThenable.js#L80
if (Array.isArray(fiber.dependencies._debugThenableState)) {
return fiber.dependencies._debugThenableState;
}
return fiber.dependencies._debugThenableState.thenables;
}
return [];
};

/**
* Traverses up or down a {@link Fiber}'s Thenables, return `true` to stop and select the current and previous props value.
*/
export const traverseThenables = (
fiber: Fiber,
selector: (
prev?: ThenableData,
next?: ThenableData,
// biome-ignore lint/suspicious/noConfusingVoidType: may or may not exist
) => boolean | void,
): boolean => {
try {
const nextThenables = getThenables(fiber);
const prevThenables = fiber.alternate ? getThenables(fiber.alternate) : [];

const maxLength = Math.max(nextThenables.length, prevThenables.length);

for (let i = 0; i < maxLength; i++) {
if (selector(prevThenables[i], nextThenables[i]) === true) return true;
}
} catch {}
return false;
};

/**
* Returns `true` if the {@link Fiber} has rendered. Note that this does not mean the fiber has rendered in the current commit, just that it has rendered in the past.
*/
Expand Down