useStoreMap

React hook, which subscribes to store and transforms its value with given function. Component will update only when selector function result will change

Common use case: subscribe to changes in selected part of store only

useStoreMap<State, Result>(
  store: Store<State>,
  fn: (state: State) => Result
): Result

note

Short version of useStoreMap introduced in effector-react@21.3.0

Arguments

store: Source store
fn ((state) => result): Selector function to receive part of source store

Returns

(Result)

useStoreMap<Source, Result>({
  store: Store<Source>;
  keys: any[];
  fn: (state: Source, keys: any[]) => Result;
  updateFilter?: (newResult: Result, oldResult: Result) => boolean;
  defaultValue?: Result;
}): Result

Overload used when you need to pass dependencies to react (to update items when some of its dependencies are changed)

Arguments

params (Object): Configuration object
- store: Source store
- keys (Array): This argument will be passed to React.useMemo to avoid unnecessary updates
- fn ((state, keys) => result): Selector function to receive part of source store
- updateFilter ((newResult, oldResult) => boolean): Optional function used to compare old and new updates to prevent unnecessary rerenders. Uses createStore updateFilter option under the hood
- defaultValue: Optional default value, used whenever fn returns undefined

Returns

(Result)

note

updateFilter option introduced in effector-react@21.3.0

note

defaultValue option introduced in effector-react@22.1.0

Example

This hook is useful for working with lists, especially with large ones

import {createStore} from 'effector'
import {useStore, useStoreMap} from 'effector-react'

const data = [
  {
    id: 1,
    name: 'Yung',
  },
  {
    id: 2,
    name: 'Lean',
  },
  {
    id: 3,
    name: 'Kyoto',
  },
  {
    id: 4,
    name: 'Sesh',
  },
]

const $users = createStore(data)
const $ids = createStore(data.map(({id}) => id))

const User = ({id}) => {
  const user = useStoreMap({
    store: $users,
    keys: [id],
    fn: (users, [userId]) => users.find(({id}) => id === userId),
  })

  return (
    <div>
      <strong>[{user.id}]</strong> {user.name}
    </div>
  )
}

const UserList = () => {
  const ids = useStore($ids)

  return ids.map(id => <User key={id} id={id} />)
}

Try it

Example​

Example