React Singleton Hook

Manage global state of your React app using hooks.

Installation

To use React Singleton Hook with your React app, install it as a dependency:

# If you use npm:
npm install react-singleton-hook

# Or if you use Yarn:
yarn add react-singleton-hook

This assumes that you’re using npm package manager with a module bundler like Webpack or Browserify to consume CommonJS modules.

React 18 breaking change

react-singleton-hook version 4.0.0 starts using new React DOM API and is only compatible with React 18. Please use 3.4.0 if you have to stay on lower React versions.

What is a singleton hook

• Singleton hooks very similar to React Context in terms of functionality. Each singleton hook has a body, you might think of it as of Context Provider body. Hook has a return value, it's similar to the value provided by context. Using a singleton hook from a component is like consuming a context.

• Singleton hooks are lazy. The body is not executed until the hook is called by some component or other hook. Once loaded, the hook body remains loaded forever. If you want to eager-load some Singleton hooks, use them at the top-level component of your App.

• Singleton hooks do not require a provider or a special App structure. Under the hood, it uses useState/useRef/useEffect and some less-known react features for performance and portability.

• It's possible to mix into single app Singleton hooks, React-Redux hooks api, React Context hooks and any custom hook.

Examples

convert any custom hook into singleton hook

In the code below, the user profile is not fetched until useUserProfile used by some component, and once fetched it is never reloaded again, the hook remains mounted forever into hidden component.

import  { useEffect, useState } from 'react';
import { singletonHook } from 'react-singleton-hook';
const api = { async getMe() { return { name: 'test' }; } };

const init = { loading: true };

const useUserProfileImpl = () => {
  const [profile, setProfile] = useState(init);
  useEffect(() => {
    api.getMe()
      .then(profile => setProfile({ profile }))
      .catch(error => setProfile({ error }));
  }, []);

  return profile;
};

export const useUserProfile = singletonHook(init, useUserProfileImpl);

dark/light mode switch

Whenever Configurator changes darkMode, all subscribed components are updated.

/***************    file:src/services/darkMode.js    ***************/  
import { useState } from 'react';
import { singletonHook } from 'react-singleton-hook';

const initDarkMode = false;
let globalSetMode = () => { throw new Error('you must useDarkMode before setting its state'); };

export const useDarkMode = singletonHook(initDarkMode, () => {
  const [mode, setMode] = useState(initDarkMode);
  globalSetMode = setMode;
  return mode;
});

export const setDarkMode = mode => globalSetMode(mode);


/***************    file:src/compoents/App.js    ***************/

import  React from 'react';
import { useDarkMode, setDarkMode } from 'src/services/darkMode';

const Consumer1 = () => {
  const mode = useDarkMode();
  return <div className={`is-dark-${mode}`}>Consumer1 - {`${mode}`}</div>;
};

const Consumer2 = () => {
  const mode = useDarkMode();
  return <div className={`is-dark-${mode}`}>Consumer2 - {`${mode}`}</div>;
};

const Configurator = () => {
  const mode = useDarkMode();
  return <button onClick={() => setDarkMode(!mode)}>Toggle dark/light</button>;
};

imperatively read hook state for non-react code

import { useState } from 'react';
import { singletonHook } from 'react-singleton-hook';

const initDarkMode = false;
let currentMode = initDarkMode;
let globalSetMode = () => { throw new Error(`you must useDarkMode before setting its state`); };

export const useDarkMode = singletonHook(initDarkMode, () => {
  const [mode, setMode] = useState(initDarkMode);
  globalSetMode = setMode;
  currentMode = mode;
  return mode;
});

export const setDarkMode = mode => globalSetMode(mode);
export const getDarkMode = () => currentMode;

use react-redux (or any other context) inside singletonHook

To use react-redux or any other context-based functionality, singleton hooks should be mounted under provider in your app. To do that, import SingletonHooksContainer from react-singleton-hook and mount anywhere in you app. SingletonHooksContainer must be rendered ealier then any component using singleton hook! By default you are not required to deal with a SingletonHooksContainer, we run this component internally in separate react app.

/***************    file:src/services/currentUser.js    ***************/
import { singletonHook } from 'react-singleton-hook';
import { useSelector } from 'react-redux';

const init = { loading: true };
const useCurrentUserImpl = () => {
  const session = useSelector(state => state.session);
  if (session.loading) return init;
  return session.user;
};

export const useCurrentUser = singletonHook(init, useCurrentUserImpl);

/***************    file:src/App.js    ***************/

import React from 'react';
import ReactDOM from 'react-dom';
import { SingletonHooksContainer } from 'react-singleton-hook';
import { Provider } from 'react-redux';
import store from 'src/store';
import App from 'src/views';

const app = (
  <Provider store={store}>
    <>
      <SingletonHooksContainer/>
      <App/>
    </>
  </Provider>
);

ReactDOM.render(app, document.getElementById('root'));

top-level components updated before low-level components

/***************    file:src/services/session.js    ***************/

import { useEffect, useState } from 'react';
import { singletonHook } from 'react-singleton-hook';

const initState = { loading: true };
let setSessionGlobal = () => { throw new Error('you must useSession before login'); };

const useSessionImpl = () => {
  const [session, setSession] = useState(initState);
  setSessionGlobal = setSession;
  useEffect(() => { setSession({ loggedIn: false }); }, []);
  return session;
};

export const useSession = singletonHook(initState, useSessionImpl);

export const login = (name, pass) => {
  setSessionGlobal({ loggedIn: true, user: { name: 'test' } });
};

/***************    file:src/index.js    ***************/
import React, { useEffect } from 'react';
import ReactDOM from 'react-dom';
import { login, useSession } from 'src/services/session';

const LoggedInView = () => {
  const session = useSession();
  console.log(`LoggerInView rendered with ${JSON.stringify(session)}`);
  return null;
};

const LoggedOutView = () => {
  const session = useSession();
  console.log(`LoggedOutView rendered with ${JSON.stringify(session)}`);
  return null;
};

const WaitingForSessionView = () => {
  const session = useSession();
  console.log(`WaitingForSessionView rendered with ${JSON.stringify(session)}`);
  return null;
};

const MainComponent = () => {
  const session = useSession();

  useEffect(() => {
    setTimeout(() => { login('testuser'); }, 2000);
  }, []);

  console.log(`MainComponent rendered with ${JSON.stringify(session)}`);

  if (session.loading) return <WaitingForSessionView/>;
  if (session.loggedIn) return <LoggedInView/>;
  return <LoggedOutView/>;
};


ReactDOM.render(<MainComponent/>, document.getElementById('root'));

/***************    console.log    ***************/
/*

MainComponent rendered with {"loading":true}
WaitingForSessionView rendered with {"loading":true}
MainComponent rendered with {"loggedIn":false}
LoggedOutView rendered with {"loggedIn":false}
MainComponent rendered with {"loggedIn":true,"user":{"name":"test"}}
LoggerInView rendered with {"loggedIn":true,"user":{"name":"test"}}

*/

Initial state callback

As of version 3.0, singletonHook accepts a callback that calculates initial state instead of predefined initial state. This callback is called once and only when the value is required. You can use it to calculate expensive initial values or avoid an extra render (and a state flickering) when initial state changes before any component consumes the hook:

example: subscribe components to pre-existing get/set data module

/***************    file:src/services/darkMode.js    ***************/

import { useState } from 'react';
import { singletonHook } from 'react-singleton-hook';

let isDarkMode = false; // the state of the module
let updateSubscribers = (mode) => {}; //update subscribers callback - do nothing by default

// pre-existing functions to manipulate the state
export const getDarkMode = () => isDarkMode;

export const setDarkMode = (newMode) => {
 isDarkMode = newMode;
 updateSubscribers(isDarkMode); // call updateSubscribers when setting new state
};

// new function - custom hook for components to subscribe.
// using getDarkMode as an init callback to get most relevant state
export const useDarkMode = singletonHook(getDarkMode, () => {
 const [mode, setMode] = useState(getDarkMode);
 updateSubscribers = setMode; // subscribing for further updates
 return mode;
});

/***************    file:src/index.js    ***************/

// you can call setter and getter any time
setDarkMode(true);
setInterval(() => setDarkMode(!getDarkMode()), 2000);

const App = () => {
 // component will be updated on darkMode change 
 // on first render "mode" is set to the current value getDarkMode returns
 const mode = useDarkMode();
 return <div className={`is-dark-${mode}`}>App - {`${mode}`}</div>;
};

Unmounting hooks when there are no consumers

You can pass the last optional parameter options to the singletonHook to configure if the hook should be unmounted when no one consumes it:

const useHook = singletonHook(
  initVal,
  () => { /*hook body*/ }, 
  { unmountIfNoConsumers: true }
);

React Native

To use this library with react-native you always have to mount SingletonHooksContainer manually. See how to do it in example: use react-redux (or any other context) inside singletonHook

Server Side Rendering

Singleton hooks are ignored during SSR and always return initial value.