[POC] useOnyx subscribed

[LukasMod]

Details

useOnyx now accepts a subscribed option (defaults to true)

When subscribed is false, the hook keeps its Onyx connection open (so the value stays cache-warm) but stops re-rendering the component on background writes to that key. It defers the render trigger, not the value: any render from another cause still reads the latest value via getSnapshot(), and flipping subscribed back to true (e.g. on re-focus) re-renders with the newest value.

Why

Out-of-focus screens re-render every time their underlying data churns, even when nothing is on screen. That's wasted render work. subscribed: false lets a screen pause its render reactions while staying connected, then catch up instantly when it matters again, without paying the connect/disconnect cost of tearing the subscription down and rebuilding it.

Why this implementation

• Gate onStoreChange() behind a ref, don't re-subscribe. The connect callback reads subscribedRef.current and skips onStoreChange() while paused. Toggling subscribed never re-subscribes, so we avoid the connect/reset churn a subscribe-dependency approach would cause.
• Still invalidate the snapshot cache on every write, even while paused. This is the subtle part: the value must not go stale. Because we keep invalidating and set shouldGetCachedValueRef, the next render from any cause serves the fresh value instead of a cached-stale one.
• The initial load is never paused. A cold key (storage-only, not yet in cache) mounted with subscribed: false still delivers its first value — the gate also fires while the result is 'loading', so the hook can't get stuck at loading. Only writes after the value has loaded are suppressed. Guarded by a regression test that fails without the condition.
• Catch-up on the focus flip. The ref is synced in a passive effect (so the gate only ever reflects committed renders, never an aborted concurrent render). On a false → true flip, that same effect delivers any write that was gated in the commit→effect gap, so a just-focused screen can't miss an update. No-op when nothing was gated (getSnapshot() returns the same reference and useSyncExternalStore bails out).
• Default is unchanged. subscribed defaults to true, so existing consumers behave exactly as before. Verified by perf tests (identical render counts) and a dedicated default-path test. 8 unit tests cover the option overall, including the mount-focused-then-blur production pattern.

Related Issues

GH_LINK

Linked E/App PR

Automated Tests

Manual Tests

Author Checklist

• I linked the correct issue in the ### Related Issues section above
• I linked the corresponding Expensify/App PR in the ### Linked E/App PR section above, and verified this change against it (E/App CI passed and manual testing completed)
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I tested this PR with a High Traffic account against the staging or production API to ensure there are no regressions (e.g. long loading states that impact usability).
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  • I verified that any callback methods that were added or modified are named for what the method does and never what callback they handle (i.e. toggleReport and not onIconClick)
  • I verified that the left part of a conditional rendering a React component is a boolean and NOT a string, e.g. myBool && <MyComponent />.
  • I verified that comments were added to code that is not self explanatory
  • I verified that any new or modified comments were clear, correct English, and explained "why" the code was doing something instead of only explaining "what" the code was doing.
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  • I verified the JSDocs style guidelines (in STYLE.md) were followed
• If a new code pattern is added I verified it was agreed to be used by multiple Expensify engineers
• I followed the guidelines as stated in the Review Guidelines
• I tested other components that can be impacted by my changes (i.e. if the PR modifies a shared library or component like Avatar, I verified the components using Avatar are working as expected)
• I verified all code is DRY (the PR doesn't include any logic written more than once, with the exception of tests)
• I verified any variables that can be defined as constants (ie. in CONST.js or at the top of the file that uses the constant) are defined as such
• I verified that if a function's arguments changed that all usages have also been updated correctly
• If a new component is created I verified that:
  • A similar component doesn't exist in the codebase
  • All props are defined accurately and each prop has a /** comment above it */
  • The file is named correctly
  • The component has a clear name that is non-ambiguous and the purpose of the component can be inferred from the name alone
  • The only data being stored in the state is data necessary for rendering and nothing else
  • If we are not using the full Onyx data that we loaded, I've added the proper selector in order to ensure the component only re-renders when the data it is using changes
  • For Class Components, any internal methods passed to components event handlers are bound to this properly so there are no scoping issues (i.e. for onClick={this.submit} the method this.submit should be bound to this in the constructor)
  • Any internal methods bound to this are necessary to be bound (i.e. avoid this.submit = this.submit.bind(this); if this.submit is never passed to a component event handler like onClick)
  • All JSX used for rendering exists in the render method
  • The component has the minimum amount of code necessary for its purpose, and it is broken down into smaller components in order to separate concerns and functions
• If any new file was added I verified that:
  • The file has a description of what it does and/or why is needed at the top of the file if the code is not self explanatory
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• If the main branch was merged into this PR after a review, I tested again and verified the outcome was still expected according to the Test steps.
• I have checked off every checkbox in the PR author checklist, including those that don't apply to this PR.

Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

[fabioh8010]

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Sync subscribed ref before passive effects

When a consumer flips subscribed from true to false (for example during a screen-blur render), this passive effect leaves subscribedRef.current at the old true value until after commit. Any Onyx write from a sibling layout effect or immediate microtask in that commit→effect window will pass the guard in the connection callback and call onStoreChange(), causing the off-screen/background re-render this option is meant to suppress. Syncing the ref during render or in a layout effect avoids that stale-true window.

Useful? React with 👍 / 👎.

[LukasMod]

You're right that there's a small gap. When subscribed flips from true to false, the ref only updates after React runs effects. If an Onyx write lands in that tiny window between the render committing and the effect running, the callback still sees true and triggers one re-render that ideally would have been skipped.

We're keeping it this way on purpose, for three reasons:

1. First, the damage is tiny and harmless. Worst case is one extra render, showing correct data, on a screen that just went off-screen. Compare that to the opposite direction (false to true): if the ref were stale there, a visible screen would miss fresh data, which is a real correctness bug. That direction is already handled by the catch-up in this effect. So the rule of thumb here is: when the gate is briefly wrong, it should fail by rendering too much, never by showing stale data. This window fails in the safe direction.

2. Second, the suggested fixes are worse than the problem. We can't "catch up" after the fact like we did for the focus direction, because you can't undo a render that already happened. The only real fix is updating the ref earlier. Updating it during render was already flagged as a P2 in an earlier round: with concurrent rendering, an aborted render could write false into the ref while the visible screen is still subscribed, and then a visible screen stops getting updates. useLayoutEffect would work but brings the SSR warning problem and would be the first use of that pattern in this library. Neither trade is worth it to skip one background render in case of that tiny gap.

3. Third, TanStack Query has exactly the same window in its subscribed option and ships with it unmitigated. Their subscription is only torn down when React runs the passive effect, so a query update in that same commit-to-effect gap also re-renders the component that just unsubscribed. This isn't an implementation bug on our side, it's just how useSyncExternalStore works: subscription changes always take effect when effects flush, not when the render commits.

[fabioh8010]

Yeah I think it's not worth investing on this, bringing more unecessary complexity is exactly what we want to avoid in the hook