effector 21.0.0

fork(domain: Domain, { values?, handlers? }?): Scope

Creates a fully isolated instance of application. The primary purpose of fork includes SSR (but is not limited to). Fork clones all the units and connections between them leading to completely independents copy of all logic defined within domain.


  1. domain (Domain): Original domain to clone, required
  2. values Optional object with either a mapping from store sids (babel-plugin is required to allow sid generation) to store values or a Map where keys are Store objects and values contains initial store value
  3. handlers Optional object with either a mapping from effect sids (babel-plugin is required to allow sid generation) to effect handlers or a Map where keys are Effect objects and values contains handlers


Scope object containing information about cloned domain

interface Scope {
getState<T>(store: Store<T>): T


Create two instances with independent counter state

import {
} from 'effector'
const domain = createDomain()
const inc = domain.createEvent()
const dec = domain.createEvent()
const $counter = domain
.on(inc, value => value + 1)
.on(dec, value => value - 1)
const scopeA = fork(domain)
const scopeB = fork(domain)
await allSettled(inc, {scope: scopeA})
await allSettled(dec, {scope: scopeB})
console.log($counter.getState()) // => 0
console.log(scopeA.getState($counter)) // => 1
console.log(scopeB.getState($counter)) // => -1

Try it

Support Map in values


effector 20.11.0

fork(domain: Domain, { values?: Map<Store, any> , handlers? }?): Scope

Support change effects


effector 20.16.0

Support for handlers to fork to change effect handlers for forked scope (useful for testing)

const app = createDomain()
const fetchFriends = app.createEffect<{limit: number}, string[]>({
async handler({limit}) {
/* some client-side data fetching */
return []
const user = app.createStore('guest')
const friends = app
.on(fetchFriends.doneData, (_, result) => result)
test to ensure that friends value is populated
after fetchFriends call
const testScope = fork(app, {
values: {
[user.sid]: 'alice',
handlers: {
[fetchFriends.sid]: () => ['bob', 'carol'],
/* trigger computations in scope and await all called effects */
await allSettled(fetchFriends, {
scope: testScope,
params: {limit: 10},
/* check value of store in scope */
// => ['bob', 'carol']
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