Bug

When a custom reviver is passed to createJSONStorage, it is correctly applied in getItem (via JSON.parse(str, options?.reviver)), but not in the internal createHandleSubscribe handler that fires when the underlying string storage emits a change (e.g. via a cross-tab storage event or a custom subscribe callback).

This means that if an atom value is a class instance or otherwise requires revival from the raw JSON object graph, any subscription-driven update receives a plain object instead of the revived value — causing runtime errors for callers that invoke methods on the result.

Reported in discussion #3101.

Root cause

createHandleSubscribe called JSON.parse(v || '') without forwarding options?.reviver:

// before
newValue = JSON.parse(v || '')

// after
newValue = JSON.parse(v || '', options?.reviver)

Fix

One-line change in src/vanilla/utils/atomWithStorage.ts: pass options?.reviver as the second argument to JSON.parse inside createHandleSubscribe.

Test

A new test createJSONStorage reviver is applied on subscription updates (#3101) is added to tests/react/vanilla-utils/atomWithStorage.test.tsx. It:

1. Creates a createJSONStorage with a reviver that turns plain { n: number } objects into Item class instances.
2. Renders a component that calls value.doubled() — a method that only exists on Item.
3. Simulates an external storage update via a CustomEvent.
4. Without the fix the subscription callback returns a plain object, value instanceof Item is false, and the component renders NOT_ITEM. With the fix it renders the correct doubled value.

Closes #3101