component-from-stream

component-from-stream on steroids

create a React-like component that sources its props from an observable stream and supports middleware. based on component-from-stream from recompose, with the following enhancements:

• compatible with any React-like framework,
  so long as it provides a React-like Component class, e.g. PREACT or Inferno.
• support for any number of middleware in the dispatching path,
  e.g. component-from-stream-redux.
  more info in the API section.
• support for a custom props dispatcher instead of the default dispatcher,
  i.e. customize what the stream emits.
• separation of stateless view from stateful reactive behaviour.
• life-cycle management and gated rendering from within the component's reactive behaviour:
  • automatically complete on componentWillUnmount.
  • only render when the reactive operator emits a props object,
    and render null on falsy values.

compatible with observable libraries such as RxJS or MOST

Separation of stateless view from stateful behaviour

the stateless rendering function (the component's view) is separated from the potentially stateful reactive operator (the component's behaviour) which maps the component's input stream of props to that of its rendering function.

Separation of behaviour from view has many advantages, among which:

• state can typically be confined to within a small subset of behaviours.
• views can be stateless and easily tested separately (e.g. with storybook)
• straightforward unit testing:
  • behaviours operate exclusively within streams of props = no DOM involved.
  • unit testing effort can focus on stateful unit behaviours, stateless behaviours being straightforward to validate.
• a component's behaviour typically becomes self-documenting.
• behaviours are independent of rendering framework.
• unit behaviours can be shared between components.
• for a given view, an existing component's behaviour can be extended by composing it with additional unit behaviours.

Block diagram

Example

see the full example in this directory.
run the example in your browser locally with npm run example or online here.

this example demonstrates how to implement component-from-stream Components described in terms of their view and composed behaviour.
for an example of a redux-like setup, see that in the component-from-stream-redux middleware module.

component-from-stream.ts

import createComponentFromStreamFactory, {
  ComponentFromStreamFactory, ComponentFromStreamConstructor
} from '../'
import { InfernoChildren, Component } from 'inferno'
import { from } from 'rxjs'

export { ComponentFromStreamFactory, ComponentFromStreamConstructor, Component, InfernoChildren }

// export a component-from-stream factory based on Inferno and RxJS
export default createComponentFromStreamFactory<Component<any,any>,InfernoChildren>(
  Component,
  from
)

copy-button/index.ts

import Button from './view'
import copyButtonBehaviour from './behaviour'
import componentFromStream, {
  ComponentFromStreamConstructor, Component, InfernoChildren
} from '../component-from-stream'

export default componentFromStream(Button, copyButtonBehaviour)

copy-button/behaviour.ts

import { shallowEqual, shallowMerge, pick, log } from '../utils'
import compose from 'basic-compose'
import { into } from 'basic-cursors'
import withEventHandler from 'rx-with-event-handler'
import { distinctUntilChanged, map, tap } from 'rxjs/operators'

export default compose(
  tap(log('copy-button:view-props:')),
  distinctUntilChanged(shallowEqual), // only render when necessary
  map(into('icon')(iconFromDisabled)),
  pickDistinct('disabled', 'onClick', 'icons'), // clean-up
  withToggleDisabledOnSuccess,
  withEventHandler('click')(map(into('success')(doCopyToClipboard))),
  map(shallowMerge(DEFAULT_PROPS)) // icons are not deep-copied
)

function doCopyToClipboard({ event, value }) {
  event.payload.preventDefault()
  return copyToClipboard(value) //true on success
}

function pickDistinct(...keys) {
  return compose(distinctUntilChanged(shallowEqual), map(pick(...keys)))
}

function iconFromDisabled ({ disabled, icons }: any) {
  return disabled ? icons.disabled : icons.enabled
}
// ...

each argument supplied to the above compose function is a reactive operator which implements a specific unit behaviour by generating an output stream of props from an input stream of props.

the unit behaviours are composed from bottom to top: props are processed from outside to inside, i.e. from component props to view props.

e.g. withEventHandler('click') from rx-with-event-handler adds an onClick prop and emits the extended props object whenever it receives a new input. whenever the onClick handler is called (from the rendered Component), it also adds an event prop to the emitted props object, and pipes the latter through the given event handler operator, in this case map(into('success')(doCopyToClipboard)), which copies the value prop to the clipboard and sets a success prop to true on success, false otherwise.

the resulting event can then be further processed by a downstream operator, e.g. withToggleDisabledOnSuccess, which toggles the boolean disabled prop for a brief moment whenever the success prop turns true. check the code for implementation details of this operator.

API

the component-from-stream factory is not directly exposed by this module.
instead, a higher-level factory is exposed for injecting the following dependencies:

• the base Component from a React-like library, e.g. PREACT or Inferno.
• Observable conversion functions for reactive operator support from third-party Observable libraries, e.g. RxJS or MOST.

this higher-level factory returns the required component factory after injection of the supplied dependencies. it is typically only required once in a project, the resulting component-from-stream factory being exposed to the project's other modules.

the above example illustrates the traditional instatiation of a component-from-stream, with a reactive operator that maps incoming props to view props.

the component factory may however be given additional optional arguments, for structuring more complex behaviours into self-documenting code:

• onprops dispatcher factory: a factory that returns a custom props dispatcher, e.g. to add default props, event handlers, and/or to dispatch an FSA object with props as payload.
• ...middlewares: rest arguments are middleware for dispatching.

import { Subscribable } from 'rx-subject'
export { Subscribable }

export default function createComponentFromStreamFactory
<C extends Component<N, any, any>, N>(
  ComponentCtor: new (props: any, context?: any) => C & Component<N, any, any>,
  fromESObservable: <T, O extends Subscribable<T>>(stream: Subscribable<T>) => O,
  opts?: Partial<ComponentFromStreamOptions>
): ComponentFromStreamFactory<C, N>
export default function createComponentFromStreamFactory
<C extends Component<N, any, any>, N>(
  ComponentCtor: new (props: any, context?: any) => C & Component<N, any, any>,
  fromESObservable: <T, O extends Subscribable<T>>(stream: Subscribable<T>) => O,
  toESObservable: <T, O extends Subscribable<T>>(stream: O) => Subscribable<T>,
  opts?: Partial<ComponentFromStreamOptions>
): ComponentFromStreamFactory<C, N>

export interface ComponentFromStreamFactory<C extends Component<N, any, any>, N> {
  <P = {}, Q = P, A = P>(
    render: (props: Q) => N,
    operator?: Operator<A, Q>,
    onprops?: PropsDispatcherFactory<P, A>
  ): ComponentFromStreamConstructor<C, N>
  <P = {}, A = P, Q = P, S = void>(
    render: (props: Q) => N,
    operator: Operator<S, Q>,
    onprops: PropsDispatcherFactory<P, A>,
    ...middlewares: Middleware<A>[]
  ): ComponentFromStreamConstructor<C, N>
}

export interface ComponentFromStreamOptions {}

export interface ComponentFromStreamConstructor
<C extends Component<N, any, any>, N> {
  new <P = {}, Q = P>(props?: P, context?: any): C & ComponentFromStream<N, P, Q>
}

export interface ComponentFromStream<N, P = {}, Q = P>
extends Component<N, P, ViewPropsState<Q>> {
  componentWillMount(): void
  componentWillReceiveProps(nextProps: Readonly<P>, nextContext: any): void
  componentWillUnmount(): void
  shouldComponentUpdate(
    props: Readonly<P>,
    state: Readonly<ViewPropsState<Q>>
  ): boolean
}

export interface ComponentConstructor<N> {
    new <P = {}, S = {}>(props: P, context?: any): Component<N, P, S>
}

export interface Component<N, P = {}, S = {}> {
    setState(state: Reducer<S, P> | Partial<S>, cb?: () => void): void
    render(props?: P, state?: S, context?: any): N
    props: Readonly<P>
    state: Readonly<S | null>
    context: any
}

export interface ViewPropsState<Q> {
    props: Q
}

export declare type Operator<I, O> =
  <S extends Subscribable<I>, T extends Subscribable<O>>(source$: S) => T

export declare type PropsDispatcherFactory<P, A = P> =
  <S extends Subscribable<A>>(
    dispatch: (v: A) => void,
    source$?: S
  ) => (props: P) => void

export declare type Middleware<I> = (
    dispatch: (...args: any[]) => void,
    source$?: Subscribable<I>, // raw ES Observable
    fromESObservable?: <T, O extends Subscribable<T>>(stream: Subscribable<T>) => O,
    toESObservable?: <T, O extends Subscribable<T>>(stream: O) => Subscribable<T>
  ) => (...args: any[]) => void

export declare type Reducer<A, V> = (acc: A, val: V) => A

Symbol.observable

This module expects Symbol.observable to be defined in the global scope. Use a polyfill such as symbol-observable and if necessary a Symbol polyfill. Check the symbol-observable-polyfill script for an example of how to generate the standalone polyfill, which can than be loaded from a script tag, or simply add import 'symbol-observable' at the top of your project's main file.

TypeScript

although this library is written in TypeScript, it may also be imported into plain JavaScript code: modern code editors will still benefit from the available type definition, e.g. for helpful code completion.

License

Copyright 2018 Stéphane M. Catala

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and Limitations under the License.