import { split } from "effector";

Choose one of cases by given conditions. It “splits” source unit into several events, which fires when payload matches their conditions. Works like pattern matching for payload values and external stores

Concepts

Case mode

Mode in which target case is selected by the name of its field. Case could be selected from data in source by case function or from external case store which kept current case name. After selection data from source will be sent to corresponding cases[fieldName] (if there is one), if none of the fields matches, then the data will be sent to cases.__ (if there is one).

See also:

• case store
• case function

Matching mode

Mode in which each case is sequentially matched by stores and functions in fields of match object. If one of the fields got true from store value or return of function, then the data from source will be sent to corresponding cases[fieldName] (if there is one), if none of the fields matches, then the data will be sent to cases.__ (if there is one)

See also:

• matcher store
• matcher function

Case store

Store with a string which will be used to choose the case by its name. Placed directly in match field.

split({
  source: Unit<T>
  // case store
  match: Store<'first' | 'second'>,
  cases: {
    first: Unit<T>,
    second: Unit<T>,
    __?: Unit<T>
  }
})

Case function

String-returning function which will be called with value from source to choose the case by its name. Placed directly in match field, should be pure

split({
  source: Unit<T>
  // case function
  match: (value: T) => 'first' | 'second',
  cases: {
    first: Unit<T>,
    second: Unit<T>,
    __?: Unit<T>
  }
})

Matcher store

Boolean store which indicates whether to choose the particular case or try the next one. Placed in fields of match object, might be mixed with matcher functions

split({
  source: Unit<T>
  match: {
    // matcher store
    first: Store<boolean>,
    second: Store<boolean>
  },
  cases: {
    first: Unit<T>,
    second: Unit<T>,
    __?: Unit<T>
  }
})

Matcher function

Boolean-returning function which indicates whether to choose the particular case or try the next one. Placed in fields of match object, might be mixed with matcher stores, should be pure

split({
  source: Unit<T>
  match: {
    // matcher function
    first: (value: T) => boolean,
    second: (value: T) => boolean
  },
  cases: {
    first: Unit<T>,
    second: Unit<T>,
    __?: Unit<T>
  }
})

Methods

split({ source, match, cases })

Formulae

split({ source, match, cases });

split({
  source: Unit<T>
  // case function
  match: (data: T) => 'a' | 'b',
  cases: {
    a: Unit<T>,
    b: Unit<T>,
    __?: Unit<T>
  }
})
split({
  source: Unit<T>
  // case store
  match: Store<'a' | 'b'>,
  cases: {
    a: Unit<T>,
    b: Unit<T>,
    __?: Unit<T>
  }
})
split({
  source: Unit<T>
  match: {
    // matcher function
    a: (data: T) => boolean,
    // matcher store
    b: Store<boolean>
  },
  cases: {
    a: Unit<T>,
    b: Unit<T>,
    __?: Unit<T>
  }
})

Arguments

• source: Unit which will trigger computation in split
• match: Single store with string, single function which returns string or object with boolean stores and functions which returns boolean
• cases: Object with units to which data will be passed from source after case selection

Returns

void

Examples

Basic

import { split, createEffect, createEvent } from "effector";
const messageReceived = createEvent();
const showTextPopup = createEvent();
const playAudio = createEvent();
const reportUnknownMessageTypeFx = createEffect(({ type }) => {
  console.log("unknown message:", type);
});

split({
  source: messageReceived,
  match: {
    text: (msg) => msg.type === "text",
    audio: (msg) => msg.type === "audio",
  },
  cases: {
    text: showTextPopup,
    audio: playAudio,
    __: reportUnknownMessageTypeFx,
  },
});

showTextPopup.watch(({ value }) => {
  console.log("new message:", value);
});

messageReceived({
  type: "text",
  value: "Hello",
});
// => new message: Hello
messageReceived({
  type: "image",
  imageUrl: "...",
});
// => unknown message: image

Try it

Direct match

You can match directly to store api as well:

import { split, createStore, createEvent, createApi } from "effector";

const messageReceived = createEvent();

const $textContent = createStore([]);

split({
  source: messageReceived,
  match: {
    text: (msg) => msg.type === "text",
    audio: (msg) => msg.type === "audio",
  },
  cases: createApi($textContent, {
    text: (list, { value }) => [...list, value],
    audio: (list, { duration }) => [...list, `audio ${duration} ms`],
    __: (list) => [...list, "unknown message"],
  }),
});

$textContent.watch((messages) => {
  console.log(messages);
});

messageReceived({
  type: "text",
  value: "Hello",
});
// => ['Hello']
messageReceived({
  type: "image",
  imageUrl: "...",
});
// => ['Hello', 'unknown message']
messageReceived({
  type: "audio",
  duration: 500,
});
// => ['Hello', 'unknown message', 'audio 500 ms']

Try it

split(source, match)

Formulae

split(source, match);

Arguments

1. source: Unit which will trigger computation in split
2. match (Object): Schema of cases, which uses names of resulting events as keys, and matching function*((value) => Boolean)*

Returns

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

Examples

Basic

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

Another

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

split({ source, clock?, match, cases })

It works the same as split with cases, however computations in split will be started after clock is triggered.

Formulae

split({source, clock?, match, cases})

Arguments

TBD

Examples

const options = ["save", "delete", "forward"];
const $message = createStore({ id: 1, text: "Bring me a cup of coffee, please!" });
const $mode = createStore("");
const selectedMessageOption = createEvent();
const saveMessageFx = createEffect(() => "save");
const forwardMessageFx = createEffect(() => "forward");
const deleteMessageFx = createEffect(() => "delete");

$mode.on(selectedMessageOption, (_, opt) => options.find((item) => item === opt));

split({
  source: $message,
  clock: selectedMessageOption,
  match: $mode,
  cases: {
    save: saveMessageFx,
    delete: deleteMessageFx,
    forward: forwardMessageFx,
  },
});

selectedMessageOption("delet"); // nothing happens
selectedMessageOption("delete");

Try it