index.md

category
Utilities

useMemoize

Cache results of functions depending on arguments and keep it reactive. It can also be used for asynchronous functions and will reuse existing promises to avoid fetching the same data at the same time.

::: tip The results are not cleared automatically. Call clear() in case you no longer need the results or use own caching mechanism to avoid memory leaks. :::

Usage

import { useMemoize } from '@vueuse/core'

const getUser = useMemoize(
  async (userId: number): Promise<UserData> =>
    axios.get(`users/${userId}`).then(({ data }) => data),
)

const user1 = await getUser(1) // Request users/1
const user2 = await getUser(2) // Request users/2
// ...
const user1 = await getUser(1) // Retrieve from cache

// ...
const user1 = await getUser.load(1) // Request users/1

// ...
getUser.delete(1) // Delete cache from user 1
getUser.clear() // Clear full cache

Combine with computed or asyncComputed to achieve reactivity:

const user1 = asyncComputed(() => getUser(1))
// ...
await getUser.load(1) // Will also update user1

Resolving cache key

The key for caching is determined by the arguments given to the function and will be serialized by default with JSON.stringify. This will allow equal objects to receive the same cache key. In case you want to customize the key you can pass getKey

const getUser = useMemoize(
  async (userId: number, headers: AxiosRequestHeaders): Promise<UserData> =>
    axios.get(`users/${userId}`, { headers }).then(({ data }) => data),
  {
    // Use only userId to get/set cache and ignore headers
    getKey: (userId, headers) => userId,
  },
)

::: warning For Vue 2 the key has to be a string or number :::

Customize cache mechanism

By default, the results are cached within a Map (normal object for Vue 2). You can implement your own mechanism by passing cache as options with following structure:

export interface MemoizeCache<Key, Value> {
  /**
   * Get value for key
   */
  get: (key: Key) => Value | undefined
  /**
   * Set value for key
   */
  set: (key: Key, value: Value) => void
  /**
   * Return flag if key exists
   */
  has: (key: Key) => boolean
  /**
   * Delete value for key
   */
  delete: (key: Key) => void
  /**
   * Clear cache
   */
  clear: () => void
}