redux-create-reducer

This code packaged as a node module

Usage:

1import { createReducer } from 'redux-create-reducer';
2import * as ActionTypes from '../constants/ActionTypes';
3
4const initialState = [];
5
6export const todos = createReducer(initialState, {
7  [ActionTypes.ADD_TODO](state, action) {
8    const text = action.text.trim();
9    return [...state, text];
10  },
11
12  [ActionTypes.REMOVE_TODO](state, action) {
13    return state.filter((_, i) => i !== action.index);
14  }
15
16  // All other action types result in state being returned
17})

Typescript typings

This library also provides powerful typescript typings when using Action classes:

1interface Action {
2  type: string;
3}
4
5interface State {
6  value: number;
7}
8
9class Reset implements Action {
10  readonly type = 'Reset Action';
11}
12class AddOne implements Action {
13  readonly type = 'AddOne Action';
14}
15class AddCustom implements Action {
16  readonly type = 'AddCustom Action';
17  constructor(public readonly value: number) { }
18}
19
20type Actions = Reset | AddOne | AddCustom;
21
22const reducer = createReducer<State, Actions>({ value: 0 }, {
23  'Reset Action': (state, action) => ({ value: 0 }),
24  'AddOne Action': (state, action) => ({ value: state.value + 1 }),
25  'AddCustom Action': (state, action) => ({ value: state.value + action.value }),
26});
27
28// If you wanted to exclude some actions you can use the `Exclude` type.
29type ActionsWithoutAddOne = Exclude<Actions, AddOne>
30const reducerThatDoesNotHandleAddOne = createReducer<State, ActionsWithoutAddOne>({ value: 0 }, {
31  'Reset Action': (state, action) => ({ value: 0 }),
32  'AddCustom Action': (state, action) => ({ value: state.value + action.value }),
33});

Stackblitz

Removing 'Reset Action': (state, action) => ({ value: 0 }), in the reducer causes the error: Property '"Reset Action"' is missing in type .... Similarly, adding 'Nonexisting Action': (state, action) => ({ value: 0 }), causes the type error: Object literal may only specify known properties, and ''Nonexisting Action'' does not exist in type 'Handlers<State, Actions>'.ts(2345)