0.3.1 • Public • Published

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    A tiny (512 byte) virtual DOM template engine for embedded projects

    IE / Edge IE / Edge Firefox Firefox Chrome Chrome Safari Safari Opera Opera iOS Safari iOS Safari Chrome for Android Chrome for Android
    Edge 14+ 45+ 49+ 10+ 37+ 10.2+ 55+

    .dom borrows some concepts from React.js (such as the re-usable Components and the Virtual DOM) and tries to replicate them with the smallest possible footprint, exploiting the ES6 javascript features.

    Why? Because with such library you can create powerful GUIs in tight space environments, such as IoT devices, where saving even an extra byte actually matters!


    • Tiny by design : The library should never exceed the 512 bytes in size. The goal is not to have yet another template engine, but to have as many features as possible in 512 bytes. If a new feature is needed, an other must be sacraficed or the scope must be reduced.

    • Built for the future : The library is heavily exploiting the ES6 specifications, meaning that it's not supported by older browsers. Currently it's supported by the 90% of the browsers in the market, but expect this to be close to 100% within the next year.

    • Declarative : Describe your HTML DOM in a structured, natural manner, helping you create powerful yet readable user interfaces.

    • Component-Oriented : Just like React.js, .dom promotes the use of functional components.

    • "Write less" accelerators : The library API is designed specifically to have short function names and accelerators, allowing you to describe your views with less code.

    Projects Using .dom

    Are you using .dom in your project? Fork this repository and add yours on the list!


    For minimum footprint, include dotdom.min.js.gz (512b) to your project.

    <script src="dotdom.min.js.gz" />

    Alternatively you can just include the minified version of the library directly before your script. Just copy-paste the minified code.


    If you already know React.js, the following examples can help you understand how the .dom primitives relate to React.

    1. Plain DOM

    Rendering a very simple DOM structure.

    React .dom
      React.createElement('div', null, 'Hello world'),
      H('div', 'Hello world'),

    2. Stateless Component

    Creating a component on which you can pass properties.

    React .dom
    function Hello(props) {
        return React.createElement(
          'div', null, `Hello ${props.toWhat}`
    ReactDOM.render( React.createElement( Hello, {toWhat: 'World'}, null ), document.body );
    function Hello(props) {
      return H('div', `Hello ${props.toWhat}`);
    R( H(Hello, {toWhat: 'World'}), document.body )

    3. Stateful Component

    Creating components that can maintain their own state.

    React .dom
    class Clickable extends React.Component {
      constructor() {
        this.state = {
          clicks: 0
    render() { const {clicks} = this.state;
    return React.createElement( 'button', { onClick() { this.setState({clicks: clicks+1}) } }, `Clicked ${clicks} times` ); } }
    ReactDOM.render( React.createElement('div', null, React.createElement(Clickable, null, null), React.createElement(Clickable, null, null) ), document.body );
    function Clickable(props, state, setState) {
      const {clicks=0} = state;
    return H('button', { onclick() { setState({clicks: clicks+1}) } }, `Clicked ${clicks} times` ); }
    R( H('div', H(Clickable), H(Clickable) ), document.body )

    4. Life-Cycle Component Events

    The component can also subscribe to life-cycle events:

    React .dom
    class WithLifeCycle extends React.Component {
      constructor() {
        this.state = {
          mounted: "no"
    componentDidMount() { this.setState({ mounted: "yes" }) }
    render() { const {mounted} = this.state;
    return React.createElement( 'div', null, `mounted = ${mounted}` ); } }
    ReactDOM.render( React.createElement('div', null, React.createElement(WithLifeCycle, null, null), ), document.body );
    function WithLifeCycle(props, state, setState, hooks) {
      const {mounted = "no"} = state;
      hooks.m.push(() => {
        setState({ mounted: "yes" })
    return H('div', `mounted = ${mounted}` ); }
    R( H('div', H(WithLifeCycle)), document.body )

    5. Keyed Updates

    Keyed updates is a useful reconciliation feature from React that enables the rendering engine to take smart decisions on which elements to update.

    A particularly useful case is when you are rendering a dynamic list of elements. Since the rendering engine does not understand which element has changed, it ends-up with wrong updates.

    To solve this issue, the VDOM engines use a key property that uniquely identifies an element in the tree. However .dom solves it, by keeping a copy of the element state in the VDom element instance itself.

    This means that you don't need any key property, just make sure you return the same VDom instance as before.

    If you are creating dynamic elements (eg. an array of vdom elements), .dom might have trouble detecting the correct update order.

    React .dom
    class Clickable extends React.Component {
      constructor() {
        this.state = {
          clicks: 0
    render() { const {clicks} = this.state; const {ket} = this.props;
    return React.createElement( 'button', { onClick() { this.setState({clicks: clicks+1}) } }, `clicks=${clicks}, key=${key}` ); } }
    const list = ["first", "second", "third"]; const components = => React.createElement(Clickable, {key}, null);
    ReactDOM.render( React.createElement('div', null, components ), document.body );
    function Clickable(props, state, setState) {
      const {clicks=0} = state;
      const {key} = props;
    return H('button', { onclick() { setState({clicks: clicks+1}) } }, `clicks=${clicks}, key=${key}` ); }
    const list = ["first", "second", "third"]; const components = => H(Clickable, {key});
    R( H('div', components), document.body )

    Note that the solution above will correctly update the stateful components, even if their order has changed. However, if you want the complete, React-Like functionality that updates individual keys, you can use the Keyed plug-in.

    function Container(props, state) {
      const {components} = props;
      // The function `K` accepts the component state and an array of components that
      // contain the `key` property, and returns the same array of components, with their
      // state correctly manipulated.
      return H("div", K(state, components));

    6. Raw (Unreconciled) Nodes

    You can create raw (unreconciled) VDom nodes (eg. that carry an arbitrary HTML content) by setting the .r property of the hooks object to any truthy value.

    This will disable further reconciliation to the child nodes, and therefore keep your contents intact.

    function Description(props, state, setState, hooks) {
      const { html } = props;
      hooks.r = 1; // Enable raw mode
      return H('div', {
        innerHTML: html

    API Reference

    Render R( VNode, DOMElement )

    R( H('div', 'Hello'), document.body )

    Renders the given VNode tree to the given DOM element. Further updates from stateful components will only occur on their immediate children.

    Create Element H( tagName | function, [properties], [children ...])

    H( 'tag' )
    H( 'tag', {prop: "value"})
    H( 'tag', H( 'child' ))
    H( 'tag', {prop: "value"}, H( 'child' ))
    H( Component, {prop: "value"} )

    Creates a VNode element. If a string is passed as the first argument, it will create a HTML element. If a function is given, it will create a stateful component.

    Properties and children are optional and they can be omitted.

    Functional Components

    Instead of a tag name you can provide a function that returns a Virtual DOM according to some higher-level logic. Such function have the following signature:

    const Component = (props, state, setState, hooks) {
      // Return your Virtual DOM
      return div( ... )

    The props property contains the properties object as given when the component was created.

    The state is initialized to an empty object {} and it's updated by calling the setState({ newState }) method. The latter will also trigger an update to the component and it's children.

    You can also assign properties to the state object directly if you don't want to cause an update.

    The hooks object can be used when you want to register handlers to the component life-cycle methods.

    Component Life-Cycle

    Similar to React, the .dom components have a life-cycle:

    • They are mounted when their root DOM element is placed on the document.
    • They are unmounted when their root DOM element is removed from the document.
    • The yare updated when the state, the properties, or the rendered DOM has changed.

    To access the life-cycle methods you need to use the fourth argument on your component function. More specifically you have to push your handling function in either of the following fields:

    const Component = (props, state, setState, hooks) {
      hooks.m.push((domElement) => {
        // '.m' is called when the component is mounted
      hooks.u.push(() => {
        // `.u` is called when the component is unmounted
      hooks.d.push((domElement, previousDomElement) => {
        // `.d` is called when the component is updated

    Tag Shorthand tag( [properties], [children ...] )

    const {div, span, a} = H;
    div( 'hello', span( 'world' ) )
    div( 'click', a({href: '#'}, 'Here'), 'to continue')

    A shorthand function can be extracted as a property from the H function. Such shorthands behave exactly like H, but with the tag name already populated.

    It's recommended to use a deconstructuring assignment in the beginning of your script in order to help javascript minifiers further optimize the result:

    const {div, span, a, button} = H;

    Tag + Class Shorthand tag.class( [properties], [children ...] )

    const {h1, span, p} = H;
    h1.short( 'short header', span.strong( 'strong text' ) )
    button.primary({onclick: handleClick}, 'Primary Action')
    p.bold.italic( twitterPost )

    Instead of providing the className as a property, you can use the .className shorthand in combination with the shorthand tag methods.

    This is the same as calling div({className: 'className'}) and the function interface is exactly the same as above.

    Note: You can add more than one class by concatenating more than one .class to the tag. For example: is the same as div({className: 'foo bar'}).


    Since the project's focus is the small size, it is lacking sanity checks. This makes it susceptible to errors. Be very careful with the following caveats:

    • You cannot trigger an update with a property removal. You must set the new property to an empty value instead. For example:

      // Wrong
      R(div({className: 'foo'}), document.body);
      R(div({}), document.body);
      // Correct
      R(div({className: 'foo'}), document.body);
      R(div({className: ''}), document.body);
    • You must never use a property named $ in your components. Doing so, will make the property object to be considered as a Virtual DOM Node and will lead to unexpected results.

      // *NEVER* do this!
      R(H(MyComponent, {$: 'Foo'}), document.body)

    Plugin Reference

    Keyed Update List K(state, components)

    In plugin-keyed.min.js

    Ensures the state of the components in the list is synchronized, according to their key property. This enables you to do react-like keyed updates like so:

    function ValueRenderer(...) { 
    function MyComponent(props, state) {
      const { values } = props;
      const components = => {
        H(ValueRenderer, {
          key: value,
          value: value
      // Synchronize state of components, based on their key
      return H('div', K(state, components))


    Are you interested in contributing to .dom? You are more than welcome! Just be sure to follow the guidelines:

    1. Install a local development environment (you will need node.js 6.x or later)
    npm install
    1. Always run the following when you think you are ready for a pull request:
    npm test && npm run build && ls -l dotdom.min.js.gz
    1. If tests pass and the size of dotdom.min.js.gz is smaller than or equal to 512 bytes, create a pull request. Otherwise reduce your scope or think of another implementation in order to bring it back down to 512 bytes.

    2. Make sure to properly comments your code, since you will most probably have to do some extreme javascript hacking. The gudeliens are the following:

     * Functions are commented as JSDoc blocks
     * @param {VNode|Array<VNode>} vnodes - The node on an array of nodes to render
     * ...
    global.R = render = (
      vnodes,                                                           // Flat-code comments start on column 70 and
      dom,                                                              // wrap after column 120.
      /* Logical separations can be commented like this */


    Licensed under the Apache License, Version 2.0


    npm i dot-dom

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