[BartekObudzinski]

Details

useOnyxState keeps its last result per hook instance, so ten components reading the same derived value compute it ten times. This PR adds two ways to share that work.

1. useOnyxState shares a stable selector's result between instances. When several components pass the same module-level selector over the same dependency references, it runs once and the rest reuse its result. Inline selectors are new functions on every render, so they behave as before. A run that read previousState, or saw it missing, is never shared, because it depends on its own instance.
2. createDerivedValue({dependencies, compute}) defines a value at module level that is computed once per change for every hook that reads it, including inline and per-ID selectors like (state) => reportNames.get(state)[reportID]. compute gets the previous dependencies and result, so an expensive value can update only what changed. previous.keep() leaves everything as it was, for a compute that has to wait (say for translations) or that failed, so the next read tries again.

Onyx.clear drops both caches, so nothing from a signed-out account stays in memory.

Selector runs per 10 writes in a Jest harness with 9,000 cards and all card list consumers mounted:

Variant	Unassigned cards change	Card renamed
useOnyxState, no sharing	90	90
Shared stable selector (this PR)	20	20

I also moved the report attributes cache from the useOnyxState port of REPORT_ATTRIBUTES onto createDerivedValue (local only, not part of this PR). Its hand-written module cache becomes the compute function, the existing tests pass, and the work stays the same with 5,000 reports: one compute per change, 5,000 report names on a start without a snapshot, none with one.

These change how much work runs, not timing. I could not get clean timing numbers on my machine.

Related Issues

Expensify#862

Linked E/App PR

None yet. This targets the useOnyxState branch, which has no E/App PR pinned to it. The report attributes port was tested locally against a build of this branch.

Automated Tests

tests/unit/useOnyxStateTest.tsx, "sharing results between instances":

1. A stable selector runs once per change for three instances.
2. Inline selectors still run in every instance.
3. The same selector over different dependency lists is not shared.
4. A run that read previousState is not shared.
5. A run made without previousState is not handed to an instance that has one.

tests/unit/createDerivedValueTest.tsx:

1. One compute per change for three components reading it through inline selectors.
2. compute gets the previous dependencies and result and updates only the changed member.
3. No compute while the dependency references stay the same.
4. The previous dependencies move forward after a compute that returned the same result.
5. After keep, every read runs again and the next compute diffs against the last real one.
6. After a throw, the next read retries from the last good result.
7. reset, also called from inside compute, starts from scratch.
8. Onyx.clear starts it from scratch.

Manual Tests

1. Build this branch (npm run build) and copy dist into an App checkout on the useOnyxState branch.
2. Move a derived value onto createDerivedValue and run its tests, then count computes with and without the change.

Not run on devices yet.

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).
• I included screenshots or videos for tests on all platforms
• I ran the tests on all platforms & verified they passed on:
  • Android / native
  • Android / Chrome
  • iOS / native
  • iOS / Safari
  • MacOS / Chrome / Safari
• I verified there are no console errors (if there's a console error not related to the PR, report it or open an issue for it to be fixed)
• I followed proper code patterns (see Reviewing the code)
  • 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.
  • I verified proper file naming conventions were followed for any new files or renamed files. All non-platform specific files are named after what they export and are not named "index.js". All platform-specific files are named for the platform the code supports as outlined in the README.
  • 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
• If the PR modifies a generic component, I tested and verified that those changes do not break usages of that component in the rest of the App (i.e. if a shared library or component like Avatar is modified, I verified that Avatar is working as expected in all cases)
• 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

🤖 Generated with Claude Code