FSA Actions, Reducers, Matchers and RxJS Utils

This TypeScript library provides:

• Factories for creating fully-typed FSA-compliant Actions.
• Composable reducers and Action filters.
• RxJS operators for easier async Effects set-up.
• @ngrx/store lazy MemoizedSelector

export type Meta = Readonly<object> & { readonly [key: string]: any };

export interface Action<P, M extends Meta = Meta> {
  readonly type: string;
  readonly payload: P;
  readonly meta: M;
  readonly error: boolean;
}

Installation

npm i rx-fsa

/ngrx and /rxjs libs are compatible with Angular 6 and RxJS 6.

Usage

Basic Empty and Syncronous Actions

import { actionCreatorFactory } from "rx-fsa/actions";

const counterActionFactory = actionCreatorFactory("COUNTER");
const resetCounterFactory = counterActionFactory("RESET");
const resetActionAction = resetCounterFactory(undefined);

const incrementCounterFactory = counterActionFactory<number>("INCREMENT");
const incrementOneAction = incrementCounterFactory(1);

const decrementCounterFactory = counterActionFactory<number>("INCREMENT");
const decrementAction = (count: number) => decrementCounterFactory(count);

Async Action Creators

interface State {
  readonly count?: number;
}

const saveCountFactory = counterActionFactory.async<State, void, Error>("SAVE");
const saveCountStartedAction = saveCountFactory.started({ count: 100 });
const saveCountDoneAction = saveCountFactory.done({ result: 100, params: { count: 100 } });
const saveCountFailedAction = saveCountFactory.failed({ error: new Error("File not saved."), params: { count: 100 } });

---

Reducers

import { caseFn, Re, reducerDefaultFn } from "rx-fsa/reducers";

const INIT_STATE: State = { count: 0 };

const resetHandler: Re<State, void> = state => INIT_STATE;

const incrementHandler: Re<State, number> = (state, add) => ({
  count: state.count + add,
});

const decrementHandler: Re<State, number> = (state, sub) => ({
  count: state.count - sub,
});

export const reducers = reducerDefaultFn(INIT_STATE)(
  caseFn(incrementCounterFactory, incrementHandler),
  caseFn(decrementCounterFactory, decrementHandler),
  caseFn(resetCounterFactory, resetHandler),
);

---

RxJS Operators

The following operators are provided under rx-fsa/rxjs:

• filterConcatAsync
• filterExhaustAsync
• filterMergeAsync
• filterSwitchAsync
• filterConcat
• filterExhaust
• filterMerge
• filterSwitch
• filterActions

Example with NgRx Effects:

import { filterExhaustAsync } from "rx-fsa/rxjs";

@Effect()
public saveCount$ = this.action$.pipe(
    filterExhaustAsync(saveCountFactory, params => this.httpSvc.save(params)),
);

The above is equivalent to:

@Effect()
public saveCount$ = this.action$.pipe(
  filter(saveCountFactory.started.match),
  mergeMap((result: R) => this.httpSvc.save(params).pipe(
    map(result = saveCountFactory.done({ result, params })),
    catchError(error => saveCountFactory.failed({ error, params }),
  ),
);

---

Lazy Selector

Create a MemoizedSelector that will emit a store slice or, if unavailable, dispatch action(s) to set the store slice and then emit.

// selectors.ts
import { createSelector } from "@ngrx/store";
import { composeLazySelector, createLazySelector } from "rx-fsa/ngrx";

const selectFeature = (state: AppState) => state.feature;
const selectFeatureCount = createSelector(selectFeature, state => state.counter);

export const lazySelectFeatureCount = createLazySelector(selectFeatureCount, loadFeatureAction.started(undefined));
export const lazySelectCountPlusN = composeLazySelector(lazySelectFeatureCount, lazySelectN)((count, n) => count + n);

// app.component.ts
import { lazySelectFeatureCount } from './selectors';

@Component({ ... })
class MyAppComponent {
  count: Observable<number>;

  constructor(private store$: Store<AppState>) {
    const selectFeatureCount = lazySelectFeatureCount(this.store$);
    this.count = this.store$.pipe(selectFeatureCount());
  }
}

API

API Documentation is coming soon. The library is small enough to scour through in GitHub to learn more.

Credits

This library was inspired by:

• https://github.com/aikoven/typescript-fsa
• https://github.com/dphilipson/typescript-fsa-reducers