HTM (Hyperscript Tagged Markup)

htm is JSX-like syntax in plain JavaScript - no transpiler necessary.

Develop with React/Preact directly in the browser, then compile htm away for production.

It's built using Tagged Templates and the browser's HTML parser.

`htm` by the numbers:

🐣 700 bytes when used directly in the browser

⚛️ 500 bytes when used with Preact (thanks gzip 🌈)

🏅 0 bytes when compiled using babel-plugin-htm

Syntax: like JSX but also lit

The syntax is inspired by lit-html, but includes features familiar to anyone who works with JSX:

Rest spread: <div ...${props}>
Self-closing tags: <div />
Components: <${Foo}> (where Foo is a component reference)
Boolean attributes: <div draggable />

Improvements over JSX

htm actually takes the JSX-style syntax a couple steps further!

Here's some ergonomic features you get for free that aren't present in JSX:

No transpiler necessary
HTML's optional quotes: <div class=foo>
HTML's self-closing tags: <img src=${url}>
Optional end-tags: <section><h1>this is the whole template!
Component end-tags: <${Footer}>footer content<//>
Support for HTML comments: <div></div>
Syntax highlighting and language support via the lit-html VSCode extension.

Project Status

The original goal for htm was to create a wrapper around Preact that felt natural for use untranspiled in the browser. I wanted to use Virtual DOM, but I wanted to eschew build tooling and use ES Modules directly.

This meant giving up JSX, and the closest alternative was Tagged Templates. So, I wrote this library to patch up the differences between the two as much as possible. As it turns out, the technique is framework-agnostic, so it should work great with most Virtual DOM libraries.

Installation

htm is published to npm, and accessible via the unpkg.com CDN:

via npm:

npm i htm

hotlinking from unpkg: (no build tool needed!)

import htm from 'https://unpkg.com/htm?module'
const html = htm.bind(React.createElement);

// just want htm + preact in a single file? there's a highly-optimized version of that:
import { html, render } from 'https://unpkg.com/htm/preact/standalone.mjs'

Usage

Since htm is a generic library, we need to tell it what to "compile" our templates to.

The target should be a function of the form h(tag, props, ...children) (hyperscript), and can return anything.

// this is our hyperscript function. for now, it just returns a description object.
function h(tag, props, ...children) {
  return { tag, props, children };
}

To use that h() function, we need to create our own html tag function by binding htm to our h() function:

import htm from 'htm';

const html = htm.bind(h);

Now we have an html() template tag that can be used to produce objects in the format we created above.

Here's the whole thing for clarity:

import htm from 'htm';

function h(tag, props, ...children) {
  return { tag, props, children };
}

const html = htm.bind(h);

console.log( html`<h1 id=hello>Hello world!</h1>` );
// {
//   tag: 'h1',
//   props: { id: 'hello' },
//   children: ['Hello world!']
// }

Example

Curious to see what it all looks like? Here's a working app!

It's a single HTML file, and there's no build or tooling. You can edit it with nano.

<!DOCTYPE html>
<html lang="en">
  <title>htm Demo</title>
  <script type="module">
    import { html, Component, render } from 'https://unpkg.com/htm/preact/standalone.mjs';

    class App extends Component {
      addTodo() {
        const { todos = [] } = this.state;
        this.setState({ todos: todos.concat(`Item ${todos.length}`) });
      }
      render({ page }, { todos = [] }) {
        return html`
          <div class="app">
            <${Header} name="ToDo's (${page})" />
            <ul>
              ${todos.map(todo => html`
                <li>${todo}</li>
              `)}
            </ul>
            <button onClick=${() => this.addTodo()}>Add Todo</button>
            <${Footer}>footer content here<//>
          </div>
        `;
      }
    }
		  
    const Header = ({ name }) => html`<h1>${name} List</h1>`

    const Footer = props => html`<footer ...${props} />`

    render(html`<${App} page="All" />`, document.body);
  </script>
</html>

Here's a live version.

Here is a Sandbox you can play with

How nifty is that? Notice there's only one import - here we're using the prebuilt Preact integration since it's easier to import and a bit smaller.

The same example works fine without the prebuilt version, just using two imports:

import { h, Component, render } from 'preact';
import htm from 'htm';

const html = htm.bind(h);

render(html`<${App} page="All" />`, document.body);

Other Uses

Since htm is designed to meet the same need as JSX, you can use it anywhere you'd use JSX.

Generate HTML using vhtml:

import htm from 'htm';
import vhtml from 'vhtml';

const html = htm.bind(vhtml);

console.log( html`<h1 id=hello>Hello world!</h1>` );
// '<h1 id="hello">Hello world!</h1>'

Webpack configuration via jsxobj: (details here)

import htm from 'htm';
import jsxobj from 'jsxobj';

const html = htm.bind(jsxobj);

console.log(html`
  <webpack watch mode=production>
    <entry path="src/index.js" />
  </webpack>
`);
// {
//   watch: true,
//   mode: 'production',
//   entry: {
//     path: 'src/index.js'
//   }
// }

qiansr/htm