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split(event, cases)

Pattern matching method, splits event into several, which fire upon source event matches its comparator function.

Arguments

1. event (Event): Array of events to be merged.
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 mathes 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: the only 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,
  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("short"); // => medium message 'short!'
message("medium"); // => medium message 'medium'
message("long message"); // => medium message 'long message' (uh-oh)

Try it