stack/packages/mosaic/framework/skills/vueuse-functions/references/useStorage.md

category, related

category	related
State	useLocalStorage, useSessionStorage, useStorageAsync

useStorage

Create a reactive ref that can be used to access & modify LocalStorage or SessionStorage.

Uses localStorage by default, other storage sources be specified via third argument.

Usage

::: tip When using with Nuxt 3, this function will NOT be auto imported in favor of Nitro's built-in useStorage(). Use explicit import if you want to use the function from VueUse. :::

import { useStorage } from '@vueuse/core';

// bind object
const state = useStorage('my-store', { hello: 'hi', greeting: 'Hello' });

// bind boolean
const flag = useStorage('my-flag', true); // returns Ref<boolean>

// bind number
const count = useStorage('my-count', 0); // returns Ref<number>

// bind string with SessionStorage
const id = useStorage('my-id', 'some-string-id', sessionStorage); // returns Ref<string>

// delete data from storage
state.value = null;

Merge Defaults

By default, useStorage will use the value from storage if it is present and ignores the default value. Be aware that when you are adding more properties to the default value, the key might be undefined if client's storage does not have that key.

import { useStorage } from '@vueuse/core';
// ---cut---
localStorage.setItem('my-store', '{"hello": "hello"}');

const state = useStorage('my-store', { hello: 'hi', greeting: 'hello' }, localStorage);

console.log(state.value.greeting); // undefined, since the value is not presented in storage

To solve that, you can enable mergeDefaults option.

import { useStorage } from '@vueuse/core';
// ---cut---
localStorage.setItem('my-store', '{"hello": "nihao"}');

const state = useStorage(
  'my-store',
  { hello: 'hi', greeting: 'hello' },
  localStorage,
  { mergeDefaults: true }, // <--
);

console.log(state.value.hello); // 'nihao', from storage
console.log(state.value.greeting); // 'hello', from merged default value

When setting it to true, it will perform a shallow merge for objects. You can pass a function to perform custom merge (e.g. deep merge), for example:

import { useStorage } from '@vueuse/core';
// ---cut---
const state = useStorage(
  'my-store',
  { hello: 'hi', greeting: 'hello' },
  localStorage,
  { mergeDefaults: (storageValue, defaults) => deepMerge(defaults, storageValue) }, // <--
);

Custom Serialization

By default, useStorage will smartly use the corresponding serializer based on the data type of provided default value. For example, JSON.stringify / JSON.parse will be used for objects, Number.toString / parseFloat for numbers, etc.

You can also provide your own serialization function to useStorage:

import { useStorage } from '@vueuse/core';

useStorage('key', {}, undefined, {
  serializer: {
    read: (v: any) => (v ? JSON.parse(v) : null),
    write: (v: any) => JSON.stringify(v),
  },
});

Please note when you provide null as the default value, useStorage can't assume the data type from it. In this case, you can provide a custom serializer or reuse the built-in ones explicitly.

import { StorageSerializers, useStorage } from '@vueuse/core';

const objectLike = useStorage('key', null, undefined, { serializer: StorageSerializers.object });
objectLike.value = { foo: 'bar' };

Type Declarations

export interface Serializer<T> {
  read: (raw: string) => T;
  write: (value: T) => string;
}
export interface SerializerAsync<T> {
  read: (raw: string) => Awaitable<T>;
  write: (value: T) => Awaitable<string>;
}
export declare const StorageSerializers: Record<
  'boolean' | 'object' | 'number' | 'any' | 'string' | 'map' | 'set' | 'date',
  Serializer<any>
>;
export declare const customStorageEventName = 'vueuse-storage';
export interface StorageEventLike {
  storageArea: StorageLike | null;
  key: StorageEvent['key'];
  oldValue: StorageEvent['oldValue'];
  newValue: StorageEvent['newValue'];
}
export interface UseStorageOptions<T>
  extends ConfigurableEventFilter, ConfigurableWindow, ConfigurableFlush {
  /**
   * Watch for deep changes
   *
   * @default true
   */
  deep?: boolean;
  /**
   * Listen to storage changes, useful for multiple tabs application
   *
   * @default true
   */
  listenToStorageChanges?: boolean;
  /**
   * Write the default value to the storage when it does not exist
   *
   * @default true
   */
  writeDefaults?: boolean;
  /**
   * Merge the default value with the value read from the storage.
   *
   * When setting it to true, it will perform a **shallow merge** for objects.
   * You can pass a function to perform custom merge (e.g. deep merge), for example:
   *
   * @default false
   */
  mergeDefaults?: boolean | ((storageValue: T, defaults: T) => T);
  /**
   * Custom data serialization
   */
  serializer?: Serializer<T>;
  /**
   * On error callback
   *
   * Default log error to `console.error`
   */
  onError?: (error: unknown) => void;
  /**
   * Use shallow ref as reference
   *
   * @default false
   */
  shallow?: boolean;
  /**
   * Wait for the component to be mounted before reading the storage.
   *
   * @default false
   */
  initOnMounted?: boolean;
}
export declare function useStorage(
  key: MaybeRefOrGetter<string>,
  defaults: MaybeRefOrGetter<string>,
  storage?: StorageLike,
  options?: UseStorageOptions<string>,
): RemovableRef<string>;
export declare function useStorage(
  key: MaybeRefOrGetter<string>,
  defaults: MaybeRefOrGetter<boolean>,
  storage?: StorageLike,
  options?: UseStorageOptions<boolean>,
): RemovableRef<boolean>;
export declare function useStorage(
  key: MaybeRefOrGetter<string>,
  defaults: MaybeRefOrGetter<number>,
  storage?: StorageLike,
  options?: UseStorageOptions<number>,
): RemovableRef<number>;
export declare function useStorage<T>(
  key: MaybeRefOrGetter<string>,
  defaults: MaybeRefOrGetter<T>,
  storage?: StorageLike,
  options?: UseStorageOptions<T>,
): RemovableRef<T>;
export declare function useStorage<T = unknown>(
  key: MaybeRefOrGetter<string>,
  defaults: MaybeRefOrGetter<null>,
  storage?: StorageLike,
  options?: UseStorageOptions<T>,
): RemovableRef<T>;