split(trigger, cases)

Pattern matching method, splits trigger unit (event, effect or store) into several events, which fires when trigger matches its comparator function.

Arguments

1. trigger (Event | Effect | Store): Event, Effect or Store unit-trigger.
2. cases (Object): Schema of cases, which uses names of resulting events as keys, and comparator function((value) => Boolean)

Returns

(Object) - Object, having keys, defined in cases argument, plus __(two underscores) - which stands for default (no matches met) case.

Example 1

import {createEvent, split} from 'effector'

const message = createEvent()

const messageByAuthor = split(message, {
  bob: ({user}) => user === 'bob',
  alice: ({user}) => user === 'alice',
})
messageByAuthor.bob.watch(({text}) => {
  console.log('[bob]: ', text)
})
messageByAuthor.alice.watch(({text}) => {
  console.log('[alice]: ', text)
})

message({user: 'bob', text: 'Hello'})
// => [bob]: Hello
message({user: 'alice', text: 'Hi bob'})
// => [alice]: Hi bob

/* default case, triggered if no one condition met */
const {__: guest} = messageByAuthor
guest.watch(({text}) => {
  console.log('[guest]: ', text)
})
message({user: 'unregistered', text: 'hi'})
// => [guest]: hi

Try it

Note: Only the first met match will trigger resulting event

Example 2

import {createEvent, split} from 'effector'

const message = createEvent()

const {short, long, medium} = split(message, {
  short: m => m.length <= 5,
  medium: m => m.length > 5 && m.length <= 10,
  long: m => m.length > 10,
})

short.watch(m => console.log(`short message '${m}'`))
medium.watch(m => console.log(`medium message '${m}'`))
long.watch(m => console.log(`long message '${m}'`))

message('Hello, Bob!')
// => long message 'Hello, Bob!'

message('Hi!')
// => short message 'Hi!'

Try it