1.0.0-beta.6 • Public • Published

    🚨 This is the README/source for the proposed Yolk v1. Go here to see the README for v0.10.1. 🚨

    Yolk https://twitter.com/patdryburgh

    Join the chat at https://gitter.im/yolkjs/yolk circle-ci npm version

    A library for building asynchronous user interfaces.

    • Familiar: Yolk is a small library built on top of Virtual DOM and RxJS. It exposes a very limited API so that you don't have to spend weeks getting up to speed. Yolk components are just plain functions that return JSX or hyperscript.

    • Everything is an observable: Yolk components consume RxJS observable streams as if they were plain values. From a websocket connection to a generator function to an event handler. If it can be represented as an observable, then it can be rendered directly into your markup.

    • Stateless: Being able to describe user interactions, control flow and plain values as observable streams means that application design becomes entirely declarative. There is no need to manually subscribe to observables in order to mutate or set component state.


    The following example renders a component with buttons to increment and decrement a counter.

    import { h, render } from 'yolk'
    import 'rxjs/add/operator/map'
    import 'rxjs/add/operator/merge'
    import 'rxjs/add/operator/scan'
    import 'rxjs/add/operator/startWith'
    function Counter ({props, children, createEventHandler}) {
      // map all plus button click events to 1
      const handlePlus = createEventHandler()
      const plusOne$ = handlePlus.map(() => 1)
      // map all minus button click events to -1
      const handleMinus = createEventHandler()
      const minusOne$ = handleMinus.map(() => -1)
      // merge both event streams together and keep a running count of the result
      const count$ = plusOne$.merge(minusOne$).scan((x, y) => x + y, 0).startWith(0)
      // prop keys are always cast as observables
      const title$ = props.title.map(title => `Awesome ${title}`)
      return (
            <button id="plus" onClick={handlePlus}>+</button>
            <button id="minus" onClick={handleMinus}>-</button>
            <span>Count: {count$}</span>
    render(<Counter title="Example" />, document.getElementById('container'))

    Additionally, see the Yolk implementation of TodoMVC or The Flux Challenge.


    The Yolk API is intentionally very limited so that you don't have to spend weeks getting up to speed. With an understanding of RxJS, you can begin building with Yolk immediately.

    Instance API

    Yolk components inject a single object as an argument. The object has three keys: props, children, and createEventHandler.

    props: Object<Observable>

    An object who's keys are the props passed into the component. These props are wrapped in observables if they are not already observables.

    import { h, render } from 'yolk'
    function MyComponent({props}) {
      return <h1>{props.title.map(t => `${t}!`)}</h1>
    // both of the following will render the same result: `<h1>Hello!</h1>`
    // render MyComponent with an observable as the title prop
    const title$ = new Rx.BehaviorSubject("Hello")
    render(<MyComponent title={title$} />, document.querySelector(`#container`))
    // render MyComponent with a plain value as the title prop
    render(<MyComponent title="Hello" />, document.querySelector(`#container`))
    children: Observable

    An observable of the children passed to a component.

    import { h, render } from 'yolk'
    function MyComponent({children}) {
      return <p>{children}</p>
    // renders <p><strong>HELLO!</strong><span>world...</span></p>
    createEventHandler(mapping: any, initialValue: any): Function

    Creates a custom subject to be used as an event handler. If the event is invoked, it is pushed to the subject as it's latest value. For example,

    import { h, render } from 'yolk'
    function MyComponent ({createEventHandler}) {
      // create an event handler
      const handleClick = createEventHandler()
      // use event handler to count the number of clicks
      const numberOfClicks =
        handleClick.scan((acc, ev) => acc + 1, 0).startWith(0)
      // create an element that displays the number of clicks
      // and a button to increment it
      return (
          <span>Number of clicks: {numberOfClicks}</span>
          <button onClick={handleClick}>Click me!</button>

    Alternatively, we could have written,

    import { h, render } from 'yolk'
    function MyComponent ({createEventHandler}) {
      // map all events to 1, and emit a value of 0 first
      const handleClick = createEventHandler(1, 0)
      const numberOfClicks =
        handleClick.scan((acc, inc) => acc + inc, 0)
      return (
          <span>Number of clicks: {numberOfClicks}</span>
          <button onClick={handleClick}>Click me!</button>

    If the first argument of createEventHandler is a function, it will be invoked with the event as the first argument.

    Subscriptions to event handlers are automatically cleaned up when the component is unmounted.

    Top Level API

    render(instance: YolkElement, node: HTMLElement): void

    Renders an instance of a YolkComponent inside of an HTMLElement.

    import { render } from 'yolk'
    render(<span>Hello World!</span>, document.querySelector(`#container`))
    h(component: string|Function , [props: Object<any>], [...children: Array<any>]): YolkElement

    If you prefer hyperscript over JSX, Yolk exposes a function h which can be used to write your components with hyperscript. h also parses tags for brevity. For example, p.my-class will append a my-class class to a p tag, #some-id will append a some-id id to a div tag.

    import { h } from 'yolk'
    function MyComponent ({createEventHandler}) {
      const handleClick = createEventHandler()
      const numberOfClicks =
        handleClick.scan((acc, ev) => acc + 1, 0).startWith(0)
      return h(`.my-counter-component`, {},
        h(`span#counter`, {}, `Number of clicks: `, numberOfClicks),
        h(`button#clicker`, {onClick: handleClick}, `Click me!`)

    See #using-jsx for how to write Yolk components with JSX.

    Using JSX

    It is highly suggested that you write Yolk with JSX. This is achieved using the Babel transpiler (version 6+). You should install your babel tool of choice (e.g., babel-cli or babel-loader) and babel-plugin-transform-react-jsx and configure the pragma option for transform-react-jsx.


    npm i --save-dev babel-cli babel-plugin-transform-react-jsx


      "plugins": [
        ["transform-react-jsx", {"pragma": "h"}]

    Then anywhere you use JSX it will be transformed into plain JavaScript. For example this,

    <p>My JSX</p>

    Turns into,

      "My JSX"

    Without this pragma, Babel will assume that you mean to write JSX for React and you will receive React is undefined errors.

    If you want to additionally transpile ES2015 code into ES5 code you should install and use babel-preset-es2015:

      "presets": ["es2015"],
      "plugins": [
        ["transform-react-jsx", {"pragma": "h"}]

    See yolk-todomvc for a complete working example.

    Supported Events

    Yolk supports the following list of standard browser events,

    onAbort onBlur onCancel onCanPlay onCanPlayThrough onChange onClick
    onCompositionStart onCompositionUpdate onCompositionEnd onContextMenu onCopy
    onCueChange onCut onDblClick onDrag onDragEnd onDragEnter onDragExit onDragLeave onDragOver
    onDragStart onDrop onDurationChange onEmptied onEnded onEncypted onError onFocus onInput
    onInvalid onKeyDown onKeyPress onKeyUp onLoad onLoadedData onLoadedMetaData onLoadStart
    onMouseDown onMouseEnter onMouseLeave onMouseMove onMouseOut onMouseOver onMouseUp
    onPaste onPause onPlay onPlaying onProgress onRateChange onReset onResize onScroll onSearch
    onSeeked onSeeking onSelect onShow onStalled onSubmit onSuspend onTimeUpdate onTouchCancel
    onTouchEnd onTouchMove onTouchStart onToggle onVolumeChange onWaiting onWheel

    In addition, Yolk supports the following custom browser events,

    onMount onUnmount

    Supported Attributes

    Yolk supports the following list of standard element attributes,

    accept acceptCharset accessKey action align alt async autoComplete autoFocus autoPlay
    autoSave bgColor border cite className color colSpan content
    contentEditable coords default defer dir dirName draggable dropZone
    encType for headers height hidden href hrefLang httpEquiv icon id isMap
    itemProp keyType kind label lang max method min name noValidate open
    optimum pattern ping placeholder poster preload radioGroup rel
    required reversed rowSpan sandbox scope span spellCheck src srcLang start
    step style summary tabIndex target title type useMap wrap allowFullScreen
    allowTransparency capture charset challenge cols contextMenu dateTime disabled form
    formAction formEncType formMethod formTarget frameBorder inputMode is list manifest
    maxLength media minLength role rows seamless size sizes srcSet width checked
    controls loop multiple readOnly selected srcDoc value


    To install Yolk, simply include it in your package.json,

    npm install yolk@1.0.0-beta.2 --save


    npm i yolk

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