import { createDuck } from 'kaczka';
const duck = createDuck('define-action-test');
const foo = duck.defineAction('FOO');
const bar = duck.defineAction('BAR');

That's it! Now you can create reducer and map your actions:

const INITIAL_STATE = { x: 0 };
const reducer = duck.createReducer(INITIAL_STATE);
reducer.withHandler(foo, s => s));
reducer.withHandler(bar, s => s);

Note: when you define an action, there's an internal property actionType added to the action creator function. Which makes the magic possible.

Also you can import a special constant ActionMatchers to match actions by a pattern:

import { createDuck, ActionMatchers } from 'kaczka';
reducer.withHandler(ActionMatchers.DEFAULT, s => s);

Right now the only supported matcher is DEFAULT, which allows you to handle all unmatched actions (as default case in plane swith/case reducer).

// flow
import { createDuck } from 'kaczka';

const duck = createDuck('define-action-test');
const foo = duck.defineAction<{ x: number }, Error>('FOO');

kaczka enforces FSA convention, for that reason you should add type for both success and error payload to your actions. Also flow will warn you when you have not handled error case in your reducer:

const INITIAL_STATE = { x: 0, events: [] };
const reducer = duck.createReducer<typeof INITIAL_STATE>(INITIAL_STATE);
reducer.withHandler(foo, (state, action) => ({
  ...state,
  x: action.payload.x, // Error doesn't have field `x`
}));

To make it pass typecheck, you need to check if it's an error action:

const INITIAL_STATE = { x: 0 };
const reducer = duck.createReducer<typeof INITIAL_STATE>(INITIAL_STATE);
reducer.withHandler(foo, (state, action) => (action.error ? {
  ...state,
  events: [...state.events, action.payload.message],
} : {
  ...state,
  x: action.payload.x,
}));

However, you may want to add a handler for positive case only, you need to use method withSuccessHandler:

const INITIAL_STATE = { x: 0 };
const reducer = duck.createReducer<typeof INITIAL_STATE>(INITIAL_STATE);
reducer.withSuccessHandler(foo, (state, action) => ({
  ...state,
  x: action.payload.x,
}));

There's also method withErrorHandler, may be handy for example to log all errors, together with ActionMatchers:

const INITIAL_STATE = { x: 0 };
const reducer = duck.createReducer<typeof INITIAL_STATE>(INITIAL_STATE);
reducer.withErrorHandler(ActionMatchers.DEFAULT, (state, action) => ({
  ...state,
  events: [...state.events, action.payload.message],
}));

You can stop typing your handlers additionally, with kaczka both action creator, and reducer handlers, will be inferred from the action definition. Also you will never forget to ...state, or other shape related errors, thanks to typing inference.

yarn add kaczka

or

npm i -S kaczka

Still work in progress, but you can find some here.

'kaczka' === toLatineLetters(translateToBelarusian('duck'));