Selective persistence
Persist user preferences while keeping temporary UI state in memory.
Zustand · Pipe
partialize
partialize is a persist option that chooses which store fields are written to storage. Return a smaller object to keep selected state across reloads while excluding transient fields.
How it works
Within persist options, partialize receives the complete store state and returns the object that should be written to storage. Returning a smaller object allows selected fields to survive reloads while transient fields and actions remain runtime-only; omitting the option uses the entire state by default.
Syntax
partialize: (state: Object) => ObjectParameters
| Name | Type | Description |
|---|---|---|
state | Object | The complete store state; the callback uses it to construct the persisted object. |
Returns
An object containing the subset of state fields to store; by default, the original state object is returned.
Key points
- partialize selects the portion of a Zustand store that persist writes to storage.
- Return an object containing only the fields that should survive persistence.
- The callback can project one field into a new persisted object.
Common mistakes
- Without partialize, the default stores the complete state object.
Example: Persist selected state
import { create } from 'zustand'
import { persist } from 'zustand/middleware'
type Store = {
token: string
theme: 'light' | 'dark'
setToken: (token: string) => void
setTheme: (theme: Store['theme']) => void
}
export const useStore = create<Store>()(
persist(
(set) => ({
token: '',
theme: 'light',
setToken: (token) => set({ token }),
setTheme: (theme) => set({ theme }),
}),
{
name: 'app-storage',
partialize: (state) => ({ theme: state.theme }),
},
),
)Persists only the theme while leaving the token and action functions out of stored data.
When to use it
Exclude sensitive or ephemeral data
Avoid writing credentials, caches, or other transient fields to storage.
Reduce persisted state
Store only the fields needed to reconstruct a feature after reload.
Interview questions
QWhat does partialize do?
partialize is a persist option typed as a function from an object state to an object. Its return value determines which state fields are stored, so returning { theme: state.theme } persists only that field.
Follow-up: What happens when the option is omitted? The identity function is used, so the complete state is selected for persistence.
QHow do you persist only part of a store?
Use partialize to return a new object containing only the fields that should be persisted. The other fields remain available in the live Zustand store but are excluded from the persisted representation.
Follow-up: How could you exclude several named fields? Build the returned object by filtering the state's entries, as shown in the documentation.
QWhere is partialize configured?
partialize belongs in the options object passed to persist, alongside settings such as the storage name. It receives the current state and returns the persisted subset.
Follow-up: What is the type of the option? (state: Object) => Object, with the identity function as its default.
Related
persiststoragehydratecreateJSONStorage