@larscom/ngrx-signals-storage

Save signal state (@ngrx/signals) to localStorage/sessionStorage and restore the state on page load.

Installation

npm install @larscom/ngrx-signals-storage

Dependencies

@larscom/ngrx-signals-storage depends on @ngrx/signals and Angular

Usage

Import withStorage function

import { withStorage } from '@larscom/ngrx-signals-storage'
import { withState, signalStore } from '@ngrx/signals'

export const CounterStore = signalStore(
  withState({
    count: 0
  }),
  // state will be saved to sessionStorage under the key: 'myKey'
  // optional config can be passed as 3th argument
  withStorage('myKey', sessionStorage, { saveIf: ({ count }) => count > 0 })
)

Configuration

export interface Config<T> {
  /**
   * These keys will not get saved to storage
   */
  excludeKeys: Array<keyof T>

  /**
   * Serializer for the state, by default it uses `JSON.stringify()`
   * @param state the last state known before it gets saved to storage
   */
  serialize: (state: T) => string

  /**
   * Deserializer for the state, by default it uses `JSON.parse()`
   * @param state the last state known from the storage location
   */
  deserialize: (state: string) => T

  /**
   * Save to storage will only occur when this function returns true
   * @param state the last state known before it gets saved to storage
   */
  saveIf: (state: T) => boolean

  /**
   * Function that gets executed on a storage error (get/set)
   * @param error the error that occurred
   */
  error: (error: any) => void
}

Common Issues

Whenever you get errors this is most likely due to serialization / deserialization of the state.

Objects like Map and Set are not serializable so you might need to implement your own serialize / deserialize function.

Example (Set)

Lets say you have a Set in your store, then you need a custom serialize / deserialize function to convert from Set to Array (serialize) and from Array to Set (deserialize)

export const MyStore = signalStore(
  withState({
    unique: new Set([1, 1, 3, 3])
  }),
  withStorage('myKey', sessionStorage, {
    serialize: (state) => JSON.stringify({ ...state, unique: Array.from(state.unique) }),
    deserialize: (stateString) => {
      const state = JSON.parse(stateString)
      return {
        ...state,
        unique: new Set(state.unique)
      }
    }
  })
)