fix(vanilla): remove Object.preventExtensions from createSnapshotDefault for Hermes compatibility

[manakuro]

Related Bug Reports or Discussions

Fixes #874

Summary

Removes Object.preventExtensions(snap) from createSnapshotDefault to fix a TypeError that occurs on React Native (Hermes).

Problem

Hermes enforces strict Proxy invariant checks. When a Proxy target is non-extensible, Hermes requires that the ownKeys trap returns every key present on the target — any mismatch throws:

TypeError: ownKeys target is non-extensible but key is missing from trap result

createSnapshotDefault calls Object.preventExtensions(snap) at the end of snapshot creation. Because Object.preventExtensions is irreversible, there is no way to undo it after the fact. The only viable fix is to not call it in the first place.

This is particularly pronounced with arrays (e.g. InformationItem[]), since their dynamic key structure ('0', '1', 'length', etc.) makes Hermes's invariant check especially strict.

The error surfaces at render time rather than at the point of assignment, because createSnapshotDefault is only called when useSnapshot runs during the render phase — not when the value is written to the store.

Note: A fix on the Hermes side is not planned. The React Native team has indicated that the Proxy API is internally discouraged at Meta. See: facebook/hermes#1609

Change

• Removed Object.preventExtensions(snap) from createSnapshotDefault

Trade-off

Removing Object.preventExtensions means snapshots are no longer guaranteed to be non-extensible. New properties could technically be added to a snapshot object at runtime. However, since snapshots are intended to be consumed as read-only values within a render cycle, this is unlikely to cause issues in practice.

Check List

• pnpm run fix for formatting and linting code and docs

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Project	Deployment	Actions	Updated (UTC)
valtio	Error		Apr 13, 2026 0:52am

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commit: 3510558

[manakuro]

The Vercel deployment is failing, but I don't have permission to view the logs. Could you please take a look?

[dai-shi]

Build Failed
No Next.js version detected. Make sure your package.json has "next" in either "dependencies" or "devDependencies". Also check your Root Directory setting matches the directory of your package.json file.

It's not your fault obviously.

[dai-shi]

Still trying to figure out #1221. But maybe I can merge this without waiting for it.

[manakuro]

Still trying to figure out #1221. But maybe I can merge this without waiting for it.

Thanks! I appreciate your help.