redux-ts-utils

Everything you need to create type-safe applications with Redux! Flux Standard Action compliant.

Example Usage

import { createStore, Store } from 'redux';
import { createAction, handleAction, reduceReducers } from 'redux-ts-utils';

// Actions

const increment = createAction<void>('increment');
const decrement = createAction<void>('decrement');
const add = createAction<number>('add');

// Reducer

type State = {
  readonly counter: number,
};

const initialState: State = {
  counter: 0,
};

const reducer = reduceReducers<State>([
  handleAction(increment, (state) => {
    state.counter += 1;
  }),
  handleAction(decrement, (state) => {
    state.counter -= 1;
  }),
  handleAction(add, (state, { payload }) => {
    state.counter += payload;
  }),
], initialState);

// Store

const store: Store<State> = createStore(reducer);
store.subscribe(() => console.log('New state!', store.getState()));

// Go to town!

store.dispatch(increment());
store.dispatch(increment());
store.dispatch(increment());
store.dispatch(decrement());
store.dispatch(add(10));
console.log('Final count!', store.getState().counter); // 12

Everything you see above is 100% type safe! The action creators only take specified types and both the state and action payloads passed to the reducers are strongly typed. Most types are inferred so you don't need to think about it most of the time, but your build will still fail if you do something you shouldn't.

The reducers are automatically run with immer, which will track any "mutations" you make and return the optimally-immutably-updated state object.

You can run the above example by cloning this repository and running the following commands:

npm install
npm run example

There is also an example React app available on GitHub which you can also see running on CodeSandbox.

API

This package exports a grand total of three functions.

A lot of the generics for these functions can be inferred (see above example). The typings below provided are optimized for readability.

createAction<T, A extends any[] = [T?]>(type: string, payloadCreator?(args: A) => T)

The createAction returns an action creator function (a function which returns an action object). The first argument should be a string representing the type of action being created, and the second argument is an optional payload creator function. The action objects returned by these action creators have two properties: type (a string) and payload (typed as T).

Typically it is best to use the simplest signature for this function:

const myActionCreator = createAction<MyActionPayload>('MY_ACTION');

The action creator function will be typed to take whatever you provide as a payload type.

If your action creator needs to take arguments other than whatever your payload is typed as you can provide types in the generic signature:

// a, b, and c are inferred below:
const addThreeNumbers = createAction<number, [number, number, number]>('ADD_THREE_NUMBERS', (a, b, c) => a + b + c);

If you need to customize the [SFP] meta property you can supply a second meta customizer function:

const addThreeNumbers = createAction<number, [number, number, number], number>(
  'ADD_THREE_NUMBERS',
  // Create `payload`
  (a, b, c) => a + b + c,
  // Create `meta`
  (a, b, c) => `${a} + ${b} + ${c}`,
);

handleAction(actionCreator, (state: Draft<State>, payload) => void, initialState?: State)

The handleAction function returns a single reducer function. The first argument should be an action creator from the createAction function. The second argument should be a "mutation" function which takes the current state and the action. The third argument is an optional initial state argument.

When provided with an action with a type that matches the type from actionCreator the mutation function will be run. The mutation function is automatically run with immer which will track all modifications you make to the incoming state object and return the optimally-immutably-updated new state object. immer will also provide you with a mapped type (Draft) of your state with all readonly modifiers removed (it will also remove Readonly mapped types and convert ReadonlyArrays to standard arrays).

reduceReducers<S>(reducers: Reducer[], initialState?: S)

The reduceReducers function takes an array of reducer functions and an optional initial state value and returns a single reducer which runs all of the input reducers in sequence.

Design Philosophy

A Strong Emphasis on Type Safety

Nothing should be stringly-typed. If you make a breaking change anywhere in your data layer the compiler should complain.

Simplicity

Whenever possible it is best to maintain strong safety; however, this can lead to extremely verbose code. For that reason this library strongly encourages type inference whenever possible.

This library exports three functions and a handful of types. Everything you need is provided by one package. The API surface is very small and easy to grok.

Not Too Opinionated

redux-ts-utils provides TypeScript-friendly abstractions over the most commonly-repeated pieces of boilerplate present in Redux projects. It is not a complete framework abstracting all of Redux. It does not dictate or abstract how you write your selectors, how you handle asynchronous actions or side effects, how you create your store, or any other aspect of how you use Redux. This makes redux-ts-utils very non-opinionated compared to other Redux utility libraries. The closest thing to an opinion you will find in this library is that it ships with immer. The reason for this is that immer has proven to be the best method for dealing with immutable data structures in a way which is both type-safe and performant. On top of that, immer, by its inclusion in redux-starter-kit, has effectively been officially endorsed as the de facto solution for managing immutable state changes. Shipping with immer helps to maintain the goal of simplicity by reducing the necessary API surface for writing reducers and by ensuring type inference whenever possible.

Setting up a redux store and middleware is typically a one-time task per project, so this library does not provide an abstraction for that. Likewise, thunks are simple but sagas are powerful, or maybe you like promises or observables. You should choose what works best for your project. Finally, given this library's strong emphasis on type safety it doesn't necessarily make sense to provide abstractions for creating selectors at the expense of type safety.

A Note on Flux Standard Actions

This library is compliant with Flux Standard Actions. That said, there is one important distinction with the way this library is typed that you should take note of of.

The FSA docs state that the payload property is optional and may have a value. This makes reducers a pain to write because TypeScript will enforce that you always check for the existence of the payload property in order to use the resulting actions. If you want to create an action that doesn't require a payload, the simplest (and most type-explicit) thing to do is to type the payload as void:

const myAction = createAction<void>('MY_ACTION');

Even with this particular distinction, the actions created by this library are FSA-compliant.

License

MIT