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Persisted signals for cascivo — sync signal state to localStorage or IndexedDB with SSR-safe initialisation. A drop-in replacement for a plain signal whenever the value should survive a reload.

Usage

import { persistedSignal } from '@cascivo/storage'

// reads the stored value on the client, falls back to the default on the server
const theme = persistedSignal('theme', 'light')

theme.value = 'dark' // written through to storage automatically

Use it exactly like a signal — read .value, assign .value, derive with useComputed. Writes are envelope-encoded (with a version stamp) and persisted for you.

SSR safety

On the server there is no storage, so persistedSignal returns the default and adopts the stored value on the client without a hydration mismatch. The returned signal carries a ready signal you can read to know when async drivers have hydrated:

const draft = persistedSignal('editor-draft', '')
draft.ready.value // false until the driver has loaded

Drivers & migrations

Choose where values live, and migrate old shapes safely when they change:

import { persistedSignal } from '@cascivo/storage'
import { indexedDBDriver } from '@cascivo/storage'

const prefs = persistedSignal(
  'prefs',
  { density: 'comfortable' },
  {
    driver: indexedDBDriver(),
    version: 2,
    migrate: (old) => ({ density: 'comfortable', ...(old as object) }),
  },
)

Available drivers: localStorageDriver (default), indexedDBDriver, and memoryDriver (tests/SSR). Drivers that support a subscribe hook propagate cross-tab updates automatically.

Install

pnpm add @cascivo/storage

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