loxia

Implementing JavaScript state machines using React Hooks.

Installation

npm install loxia

Motivation

I consider React Hooks to be particularly suitable for implementing state machines. Based on this idea, I developed a bookmark manager. It's UI makes intensive use of the Hooks and patterns developed here and serves as a real world test.

Hooks

In general, all Hooks in this library are built to be used with any React Hooks compliant implementation. That would be, for example, Batis, Preact, and of course React. In the usage examples, Batis is always used, but as an alternative, the analogous usage with React is shown as a comment.

useTransition

A transition is a function with special runtime behavior that can be used to implement the correct behavior of the transition methods of a state machine. A transition executes the passed callback once and returns true if its dependencies have not changed, so it should depend on the state of the associated state machine.

import {Host} from 'batis'; // import * as React from 'react';
import {createTransitionHook} from 'loxia';

const useTransition = createTransitionHook(Host /* React */);

function useLock(): Lock {
  const [locked, setLocked] = Host /* React */.useState(false);
  const transition = useTransition(locked);

  const lock = Host /* React */.useCallback(
    () => transition(() => setLocked(true)),
    [transition],
  );

  const unlock = Host /* React */.useCallback(
    () => transition(() => setLocked(false)),
    [transition],
  );

  return Host /* React */.useMemo(
    () => (locked ? {locked, unlock} : {locked, lock}),
    [locked],
  );
}

function createTransitionHook(hooks: BatisHooks): UseTransition;

type UseTransition = (
  ...dependencies: readonly [unknown, ...unknown[]]
) => Transition;

type Transition = (callback?: () => void) => boolean;

useBinder

A binding is a function that is tied to the life cycle of the Hook or component it surrounds. Often React components are already unmounted and an associated asynchronous operation should no longer have any effect. It is therefore useful to bind the callback functions of Promise.then, Promise.catch, and also setTimeout.

import {Host} from 'batis'; // import * as React from 'react';
import {createBinderHook} from 'loxia';

const useBinder = createBinderHook(Host /* React */);

function useExample() {
  const bind = useBinder();

  Host /* React */.useEffect(() => {
    setTimeout(
      bind(() => {
        // ...
      }),
    );
  });
}

function createBinderHook(hooks: BatisHooks): UseBinder;

type UseBinder = () => Bind;

type Bind = <TCallback extends (...args: any[]) => void>(
  callback: TCallback,
) => Binding<TCallback>;

type Binding<TCallback extends (...args: any[]) => void> = (
  ...args: Parameters<TCallback>
) => boolean;

useReceiver

A receiver is a state machine which allows the reception of a signal in the form of a promise passed as an argument. A receiver is always in one of the following states receiving, successful, or failed. As long as the reference to the passed promise remains the same, a receiver represents the state of the promise. When a reference to a new promise is passed, the old promise no longer affects the receiver state.

It makes sense to use a receiver if an asynchronous operation is based on user input. If the user input changes in the meantime and a new asynchronous operation overwrites the old one, the old one should no longer have any effect.

import {Host} from 'batis'; // import * as React from 'react';
import {createReceiverHook} from 'loxia';

const useReceiver = createReceiverHook(Host /* React */);

function useAsyncJsonData(url) {
  const signal = Host /* React */.useMemo(
    () => fetch(url).then((response) => response.json()),
    [url],
  );

  return useReceiver(signal);
}

function createReceiverHook(hooks: BatisHooks): UseReceiver;

type UseReceiver = <TValue>(signal: Promise<TValue>) => Receiver<TValue>;

type Receiver<TValue> =
  | ReceivingReceiver
  | SuccessfulReceiver<TValue>
  | FailedReceiver;

interface ReceivingReceiver {
  readonly state: 'receiving';
}

interface SuccessfulReceiver<TValue> {
  readonly state: 'successful';
  readonly value: TValue;
}

interface FailedReceiver {
  readonly state: 'failed';
  readonly error: unknown;
}

useSender

A sender is a state machine which allows to send exactly one signal at a time.

function createSenderHook(hooks: BatisHooks): UseSender;

type UseSender = () => Sender;

type Sender = IdleSender | SendingSender | FailedSender;

interface IdleSender {
  readonly state: 'idle';

  send(signal: Promise<unknown>): boolean;
}

interface SendingSender {
  readonly state: 'sending';
}

interface FailedSender {
  readonly state: 'failed';
  readonly error: unknown;

  send(signal: Promise<unknown>): boolean;
}