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observe-component

observe-component

import React from 'react';
import { render } from 'react-dom';
import { observeComponent, fromComponent } from 'observe-component/kefir';
 
const ObservableButton = observeComponent('onClick')('button');
 
function MyButton(props) {
    return (<ObservableButton>Hello</ObservableButton>);
}
 
render(<MyButton />, Document.getElementById('my-app'));
 
const clickObservable =
    fromComponent(ObservableButton);
 
clickObservable
    .onValue(() => {
        console.log('world!');
    });
 

Installation

npm install --save observe-component

You will also need to install your choice of Kefir, RxJS (v4), or RxJS (v5+), and React if they're not already a part of your project.

API

observeComponent(...events)(Component)

observeComponent(...events) returns a function that, when applied to a React component, returns a higher-order ObservableComponent with an attached observable of the specified events. Supports all events supported by React's event system.

Example:

const ObservableDiv = observeComponent('onMouseDown', 'onMouseUp')('div');

fromComponent(observeComponent, ...events)

Returns the observable attached to the ObservableComponent. Optional string event parameters can be supplied to return a observable only containing those events.

fromComponent observables emit a ComponentEvent object.

Example:

const ObservableDiv = observeComponent('onMouseDown', 'onMouseUp')('div');
 
// with the Kefir library, we can use the `log()` operator, 
// which will log all 'onMouseDown' and 'onMouseUp' events 
fromComponent(ObservableDiv).log()
 
// will only log 'onMouseUp' events 
fromComponent(ObservableDiv, 'onMouseUp').log();

ComponentEvent

The ComponentEvent object contains three properties:

  • type : a string which identifies the event that has occurred, e.g.: 'onClick', 'onScroll'
  • value : typically the React library SyntheticEvent (see: Event System)
  • props : the props of the observed component at event trigger

But why?

Because Functional Reactive Programming is pretty cool, and so is React. However, React's API is not very FRP-friendly; the necessity to wire up events by hand using buses (or subjects, in RxJS-speak) easily leads us to the Bus of Doom, and in general is finnicky and boilerplate-y to connect an observer to React.

There are also plenty of libraries for connecting observables to React, but very few (none that I've found) that transition React events to observables, enabling a fully functional reactive architecture.

Dependencies

At the moment, observe-component allows a consumer to use either Kefir, RxJS v4 or RxJS v5 for observables. Support for more FRP libraries might become available if it is highly desired. To use your choice of library, you can import like so:

/* ES6 module syntax */
// kefir.js 
import { observeComponent, fromComponent } from 'observe-component/kefir';
 
// ... 
const Button = observeComponent('onClick')('button');
const clickObservable =
    fromComponent(Button, 'onClick')
 
clickObservable
    .onValue((e) => console.log(e));
 
// => ComponentEvent { type: 'onClick', value: SyntheticEvent, props: {} } 
// RxJS v4 
import { observeComponent, fromComponent } from 'observe-component/rx';
 
// ... 
const Button = observeComponent('onClick')('button');
const clickObservable =
    fromComponent(Button, 'onClick');
 
clickObservable
    .subscribe((e) => console.log(e));
 
// => ComponentEvent { type: 'onClick', value: SyntheticEvent, props: {} } 
// RxJS v5+ 
import { observeComponent, fromComponent } from 'observe-component/rxjs';
 
// ... 
const Button = observeComponent('onClick')('button');
const clickObservable =
    fromComponent(Button, 'onClick');
 
clickObservable
    .subscribe((e) => console.log(e));
 
// => ComponentEvent { type: 'onClick', value: SyntheticEvent, props: {} } 

Examples

For these examples, I will use the Kefir library. RxJS is quite similar.

Components as stateless functions

import React, { Component } from 'react';
import { render } from 'react-dom';
import { observeComponent, fromComponent } from 'observe-component/kefir';
 
const ObservableInput = observeComponent('onChange')('input');
 
function MyApp(props) {
    return (
        <div>
            <div>Hello {this.props.name}!</div>
            <ObservableInput type="text" value={props.name} />
        </div>
    );
}
 
const nameObservable =
    fromComponent(ObservableInput)
    /* The observables values contain three properties:
        'type': The type of the event that was triggered, e.g. 'onChange'
        'value': The React library `SyntheticEvent`
        'props': the current props on the component
    */
    .map(({ value }) => value.target.value);
 
nameObservable
    .onValue((name) => 
        render(<MyApp name={name} />, document.getElementById('my-app'))
    );
 

Dynamic lists

const ObservableItem = observeComponent('onClick')('li');
 
function MyList(props) {
    return (
        <div>
            <span>Selected: { currentName }</span>
            <ul style={styles.ul}>
                {['John', 'Will', 'Marie'].map((name) => 
                    <ObservableLi key={name}>
                        { name }
                    </ObservableLi>
                )}
            </ul>
        </div>
    );
}
 
fromComponent(ObservableLi)
    .map((ev) => ev.props.children)
    .startWith('John')
    .subscribe((name) => {
        render(<App currentName={name} />, document.getElementById('app'));
    });
 

Example here

You can observable any kind of component

...as long as you pass event handlers to the appropriately. The library simply passes special handlers to React's event system (on<Event>) to abstract them into observables.

class MyWidget extends React.Component {
    render() {
        return (
            <div>
                <button onClick={this.props.onClick}>Click me!</button>
                <input onChange={this.props.onChange} defaultValue="Change me!" />
            </div>
        );
    }
}
 
const ObservableWidget = observeComponent('onClick', 'onChange')(MyWidget);
const widgetObservable = 
    fromComponent(ObservableWidget);
 
widgetObservable
    .onValue(({type, value}) => {
        if (type === 'onClick') {
            console.log('clicked');
        }
        else if (type === 'onChange') {
            console.log('changed: '+value.target.value);
        }
    });

However, you are strongly encouraged to create observables out of basic components and merge them, rather than manually pass the event handlers yourself.

Also, if we can get away with it, we'd always like to use stateless functions as components. :)

import {merge} from 'kefir';
 
// Create Observable button and Observable inputs 
const ObservableButton = observeComponent('onClick')('button');
const ObservableInput = observeComponent('onChange')('input');
 
// Component is simply a function from props to view 
function MyWidget(props) {
    return (
        <div>
            <ObservableButton>Click me!</ObservableButton>
            <ObservableInput defaultValue="Change me!" />
        </div>
    );
}
 
// We construct our application from the two observables 
const widgetObservable = 
    merge([
        fromComponent(ObservableButton),
        fromComponent(ObservableInput),
    ]);
 
widgetObservable
    .onValue(({type, value}) => {
        if (type === 'onClick') {
            console.log('clicked');
        }
        else if (type === 'onChange') {
            console.log('changed: '+value.target.value);
        }
    });

License

MIT