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Social Media Photo by Andrii Ganzevych on Unsplash
A minimalistic library to create fast and reactive Web pages.
<!doctype html>
<script type="module">
import { html } from 'https://esm.run/uhtml';
document.body.prepend(
html`<h1>Hello DOM !</h2>`
);
</script>uhtml (micro µ html) offers the following features without needing specialized tools:
- JSX inspired syntax through template literal html and svg tags
- React like components with Preact like signals
- compatible with native custom elements and other Web standards out of the box
- simplified accessibility via aria attribute and easy dataset handling via data
- developers enhanced mode runtime debugging sessions
test in codepen
import { html, signal } from 'https://esm.run/uhtml';
function Counter() {
const count = signal(0);
return html`
<button onClick=${() => count.value++}>
Clicked ${count.value} times
</button>
`;
}
document.body.append(
html`<${Counter} />`
);If you are familiar with JSX you will find uhtml syntax very similar:
- self closing tags, such as <p />
- self closing elements, such as <custom-element>...</>
- object spread operation via <${Component} ...${{any: 'prop'}} />
- key attribute to ensure same DOM node within a list of nodes
- ref attribute to retrieve the element via effects or by any other mean
The main difference between uhtml and JSX is that fragments do not require <>...</> around:
// uhtml fragment example
html`
<div>first element</div>
<p> ... </p>
<div>last element</div>
`On top of JSX like features, there are other attributes with a special meaning:
- aria attribute to simplify a11y, such as <button aria=${{role: 'button', labelledBy: 'id'}} />
- data attribute to simplify dataset handling, such as <div data=${{any: 'data'}} />
- @event attribute for generic events handling, accepting an array when options are meant to be passed, such as <button @click=${[event => {}, { once: true }]} />
- on... prefixed, case insensitive, direct events, such as <button onclick=${listener} />
- .direct properties access, such as <input .value=${content} />, <button .textContent=${value} /> or <div .className=${value} />
- ?toggle boolean attributes, such as <div ?hidden=${isHidden} />
All other attributes will be handled via standard setAttribute or removeAttribute when the passed value is either null or undefined.
Elements that contain data such as <script> or <style>, or those that contains text such as <textarea> require explicit closing tag to avoid having in between templates able to break the layout.
This is nothing new to learn, it's just how the Web works, so that one cannot have </script> within a <script> tag content and the same applies in here.
In debugging mode, an error telling you which template is malformed will be triggered in these cases.
Useful for developers but never really relevant for end users, comments are ignored by default in uhtml except for those flagged as "very important".
The syntax to preserve a comment in the layout is <!--! important !-->. Every other comment will not be part of the rendered tree.
html`
<!--! this is here to stay !-->
<!--// this will go -->
<!-- also this -->
`The result will be a clear <!-- this is here to stay --> comment in the layout without starting and closing !.
There are two kind of "logical comments" in uhtml, intended to help its own functionality:
- <!--◦--> holes, used to pin in the DOM tree where changes need to happen.
- <!--<>--> and <!--</>--> persistent fragments delimeters
The hole type might disappear once replaced with different content while persistent fragments delimeters are needed to confine and/or retrieve back fragments' content.
Neither type will affect performance or change layout behavior.
import {
// DOM manipulation
render, html, svg, unsafe,
// Preact like signals, based on alien-signals library
signal, computed, effect, untracked, batch,
// extras
Hole, fragment,
} from 'https://esm.run/uhtml';In details
- render(where:Element, what:Function|Hole|Node) to orchestrate one-off or repeated content rendering, providing a scoped effect when a function is passed along, such as render(document.body, () => App(data)). This is the suggested way to enrich any element content with complex reactivity in it.
- html and svg template literal tags to create either HTML or SVG content.
- unsafe(content:string) to inject any content, even HTML or SVG, anywhere within a node: <div>${unsafe('<em>value</em>')}</div>
- signal, computed, effect, untracked and batch utilities with Preact signals inspired API, fueled by alien-signals
- Hole class used internally to resolve html and svg tags' template and interpolations. This is exported mainly to simplify TypeScript relaed signatures.
- fragment(content:string, svg?:boolean) extra utility, used internally to create either HTML or SVG elements from a string. This is merely a simplification of a manually created <template> element, its template.innerHTML = content operation and retrieval of its template.content reference, use it if ever needed but remember it has no special meaning or logic attached, it's literally just standard DOM fragment creation out of a string.
The easiest way to start using uhtml is via CDN and here a few exported variants:
// implicit production version
import { render, html } from 'https://esm.run/uhtml';
// https://cdn.jsdelivr.net/npm/uhtml/dist/prod/dom.js
// explicit production version
import { render, html } from 'https://esm.run/uhtml/prod';
// https://cdn.jsdelivr.net/npm/uhtml/dist/prod/dom.js
// explicit developer/debugging version
import { render, html } from 'https://esm.run/uhtml/dev';
import { render, html } from 'https://esm.run/uhtml/debug';
// https://cdn.jsdelivr.net/npm/uhtml/dist/dev/dom.js
// automatic prod/dev version on ?dev or ?debug
import { render, html } from 'https://esm.run/uhtml/auto';
import { render, html } from 'https://esm.run/uhtml/cdn';
// https://cdn.jsdelivr.net/npm/uhtml/dist/prod/cdn.jsUsing https://esm.run/uhtml/cdn (or /auto) or the fully qualified https://cdn.jsdelivr.net/npm/uhtml/dist/prod/cdn.js URL provides an automatic switch to debug mode if the current page location contains ?dev or ?debug or ?debug=1 query string parameter plus it guarantees the library will not be imported again if other scripts use a different CDN that points at the same file in a different location.
This makes it easy to switch to dev mode by changing the location from https://example.com to https://example.com?debug.
Last, but not least, it is not recommended to bundle directly uhtml in your project because components portability becomes compromised, as example, if each component bundles within itself uhtml.
Another way to grant CDN and components portability is to use an import map and exclude uhtml from your bundler.
<!-- defined on each page -->
<script type="importmap">
{
"imports": {
"uhtml": "https://cdn.jsdelivr.net/npm/uhtml/dist/prod/cdn.js"
}
}
</script>
<!-- your library code -->
<script type="module">
import { html } from 'uhtml';
document.body.append(
html`Import Maps are Awesome!`
);
</script>Minification is still recommended for production use cases and not only for JS, also for the templates and their content.
The rollup-plugin-minify-template-literals is a wonderful example of a plugin that does not complain about uhtml syntax and minifies to its best uhtml templates in both vite and rollup.
This is a rollup configuration example:
import terser from "@rollup/plugin-terser";
import templateMinifier from "rollup-plugin-minify-template-literals";
import { nodeResolve } from "@rollup/plugin-node-resolve";
export default {
input: "src/your-component.js",
plugins: [
templateMinifier({
options: {
minifyOptions: {
// allow only explicit <!--! comments !-->
ignoreCustomComments: [/^!/],
keepClosingSlash: true,
caseSensitive: true,
},
},
}),
nodeResolve(),
terser(),
],
output: {
esModule: true,
file: "dist/your-component.js",
},
};The current pareser is already environment agnostic, it runs on the client like it does in the server without needing dependencies at all.
However, the current SSR story is still a work in progress but it's planned to land sooner than later.