Universal React RxJS

Create universal web apps with React and RxJS.

npm

Installation

Universal React RxJS requires React 16.8.3 or later and RxJS 6.0.0 or later.

npm i -S universal-react-rxjs

Configure the build

Important: The universal-react-rxjs package is not transpiled! Your project must transpile it.

See Webpack or Browserify instructions.

What it does

Universal React RxJS connects an observable to a component to create a widget.

A widget is a React component whose state is managed by an RxJS observable.

Widgets can also be server-side rendered asynchronously, even if they have ancestor widgets and/or descendant widgets.

Server-side rendered widgets can be hydrated, with the initial state provided by the server, so that the browser doesn't have to call any endpoints for the initial render.

Comparison to React Redux

Universal React RxJS is an alternative to React Redux, using RxJS as the state manager instead of Redux.

The two libraries have some key differences:

	React Redux	Universal React RxJS
Multiple stores/observables	Discouraged	Unopinionated
Relationship to component tree	Decoupled	Attached to a component
Asynchronous state change	Requires third-party libraries	Built-in
Server-side rendering	No	Yes

Usage

Create a context to connect an RxJS observable to your React component:

// profile-context.js
 
import React from 'react';
 
export default React.createContext(null);

Create your React component hierarchy, connecting your context to it using <Inject context={yourContext} />:

// profile.js
 
import React from 'react';
import {Inject} from 'universal-react-rxjs';
import profileContext from './profile-context';
 
function ProfileName() {
    return (
        <section className="profile__name">
            <Inject
                context={profileContext}
                compare={['isLoading', 'name']}
            >
                {({isLoading, name}) => (
                    isLoading ? (
                        <em>
                            Loading...
                        </em>
                    ) : (
                        name
                    )
                )}
            </Inject>
        </section>
    );
}
 
function ProfilePhoto() {
    return (
        <section className="profile__photo">
            <Inject context={profileContext}>
                {({isLoading, photo}) => (
                    <img
                        className="profile__photo-img"
                        src={isLoading ? '/static/img/profile-loading.gif' : photo}
                        alt={isLoading ? 'Loading profile' : 'Profile photo'}
                    />
                )}
            </Inject>
        </section>
    );
}
 
export default function Profile() {
    return (
        <section className="profile">
            <ProfileName />
            <ProfilePhoto />
        </section>
    );
}

NOTE: compare specifies how to skip widget states that are duplicates with respect to the subset of the state being used. Typically, this is just a list of the widget state properties being used. However, you can instead specify a function that compares consecutive widget states for equality.

Define your component's event stream and create a widget:

// profile-widget.js
import {combineLatest, of as observableOf} from 'rxjs';
import {map, skip, startWith, switchMap} from 'rxjs/operators';
import {widget} from 'universal-react-rxjs';
import component from './profile';
import context from './profile-context';
import fetchName from './streams/fetch-name';
import fetchPhoto from './streams/fetch-photo';
 
export default widget({
    name: 'profile',
    component,
    context,
    getData: (props$, hydration, immediate) => {
        const userId$ = props$.map(({userId}) => userId);
 
        const name$ = hydration
            ? observableOf({name: hydration.name})
            : userId$.pipe(switchMap(fetchName));
 
        const photo$ = hydration
            ? observableOf({photo: hydration.photo})
            : userId$.pipe(switchMap(fetchPhoto));
 
        return combineLatest([name$, photo$]).pipe(
            map(([name, photo]) => ({
                // React component rendered with this state as its props
                state: {name, photo},
                // Hydration data rendered alongside the React element in the HTML page
                hydration: {name, photo},
                // Additional data accumulated during server-side rendering
                data: {maxAge: 60},
            })),
            // Start with a loading state ...
            startWith({
                state: {isLoading: true},
            }),
            // ... but skip it if an immediate value isn't required
            skip(immediate ? 0 : 1)
        );
    },
});

The general contract of getData(props$, hydration, immediate) is:

Return an RxJS Observable that emits objects of the form {state, hydration, data} where both state and hydration are objects and data is any additional data you want to accumulate during server-side rendering.
If the third parameter (immediate) provided to getData is true, the observable is expected to immediately produce an event.
Events must contain hydration during server-side rendering.
Events can contain hydration and/or data client-side, but it will have no effect.
Keep hydration small to keep server-side rendered HTML pages small. Only attach the minimum amount of data required to hydrate widgets without them having to fetch data from APIs.

Somewhere on the server:

import React from 'react';
import {renderToHtml} from 'universal-react-rxjs';
import ProfileWidget from './profile-widget';
 
// Server-side render an HTML page consisting of the profiles from a list of
// user IDs.
async function renderUserProfilesPage(userIds) {
    let maxAge = 60; // Default max-age to 60s
 
    // Generate server-side rendered profile of users
    const htmlArray = await Promise.all(
        userIds.map((userId) => renderToHtml(
            <ProfileWidget userId={userId} />,
            {
                onData: (data) => {
                    // Keep the smallest non-zero maxAge
                    if (data.maxAge && data.maxAge < maxAge) {
                        maxAge = data.maxAge;
                    }
                },
            }
        ))
    );
 
    return {
        maxAge,
        html: `<body>${htmlArray.join('')}</body>`,
    };
}

When renderToHtml is called, it will call each widget's getData function, passing in an RxJS Observable that emits the widget's props (in this case, userId) every time it's rendered. When the stream returned by getData produces its first event (an object consisting of state to inject into the React component and hydration to attach to the HTML page), the widget's React component will be rendered with the state as its props and the hydration data will be rendered adjacent to it in the HTML page. The data property of the event will be passed to the onData function specified in renderToHtml, if specified at all. It is up to the onData function to accumulate data objects as it sees fit, bearing in mind that onData is called in render order, which is defined by ReactDOM.renderToString.

Somewhere on the client:

import {hydrate} from 'universal-react-rxjs';
import ProfileWidget from './profile-widget';
 
// Hydrate all instances of profile-widget on the page
hydrate(ProfileWidget);

When hydrate is called, it finds all the server-side rendered instances of the widget in the DOM, reads their attached props and hydration data, then calls getData(props$, hydration, immediate), expecting the client to render the profiles synchronously, without having to load data from APIs.

Bear in mind that widgets are just React components, so you can use them directly in JSX and you don't even need to initially render them on the server. You could even use this library just for connecting to RxJS.

Contextless form

In some situations, context is overkill, because your UI is fairly shallow and there is not much benefit, if any, to be gained by using a context. And in some cases, you may be using a component from a third-party library as the copmonent parameter. For this reason, context is optional. If you don't provide a context, the state of the stream returned by getData will be fed directly into the component's props (which otherwise doesn't receive props from widget).

import React from 'react';
 
export default function Profile({isLoading, name, photo}) {
    return (
        <section className="profile">
            <section className="profile__name">
                {isLoading ? (
                    <em>
                        Loading...
                    </em>
                ) : (
                    name
                )}
            </section>
            <section className="profile__photo">
                <img
                    className="profile__photo-img"
                    src={isLoading ? '/static/img/profile-loading.gif' : photo}
                    alt={isLoading ? 'Loading profile' : 'Profile photo'}
                />
            </section>
        </section>
    );
}

export default widget({
    name: 'profile',
    component: Profile,
    getData: (props$, hydration, immediate) => {
        // Use your imagination...
    },
    // context omitted
});

This saves you from the following additional boilerplate:

// NOTE: Don't do this!
 
const context = React.createContext(null);
 
function component() {
    return (
        <Inject context={context}>
            {(state) => (
                <Profile {...state} />
            )}
        </Inject>
    );
}
 
export default widget({
    name: 'profile',
    context,
    component,
    getData,
});

Hooks

A custom hook is provided as an alternative to <Inject />.

// profile.js
 
import React from 'react';
import {useWidgetState} from 'universal-react-rxjs';
import profileContext from './profile-context';
 
export default function Profile() {
    const {isLoading, name, photo} = useWidgetState(
        profileContext,                // same as Inject's context prop
        ['isLoading', 'name', 'photo'] // same as Inject's compare prop
    );
 
    return (
        <section className="profile">
            <section className="profile__name">
                {isLoading ? (
                    <em>
                        Loading...
                    </em>
                ) : (
                    name
                )}
            </section>
            <section className="profile__photo">
                <img
                    className="profile__photo-img"
                    src={isLoading ? '/static/img/profile-loading.gif' : photo}
                    alt={isLoading ? 'Loading profile' : 'Profile photo'}
                />
            </section>
        </section>
    );
}

Refs

Refs work as expected. Any ref passed to a widget will be forwarded to the underlying component.

function SomeComponent({userId}) {
    const profileRef = useRef(null);
 
    return (
        <ProfileWidget
            ref={profileRef} // ref forwarded to Profile
            userId={userId}
        />        
    );
}

The underlying component must be capable of taking a ref. Note: Inject is incapable of forwarding refs.

Support for styled-components

The server-side rendering portion of the above example can be updated as follows:

import React from 'react';
import {renderToHtml, StyledComponentsServerRenderer} from 'universal-react-rxjs';
import ProfileWidget from './profile-widget';
 
// Server-side render an HTML page consisting of the profiles from a list of
// user IDs.
async function renderUserProfilesPage(userIds) {
    // Generate server-side rendered profile of users
    const renderer = new StyledComponentsServerRenderer();
    const htmlArray = await Promise.all(
        userIds.map((userId) => renderToHtml(
            <ProfileWidget userId={userId} />,
            {renderer}
        ))
    );
 
    return `<head>${
        renderer.getStyleTags()
    }</head><body>${
        htmlArray.join('')
    }</body>`;
}

This uses StyledComponentsServerRenderer as an alternative renderer, which uses ServerStyleSheet from styled-components to gather rendered stylesheets.

Contributing

Contributions are welcome. See CONTRIBUTING.md in this repo for contribution guidelines.