Untrue

JavaScript library for rendering user interfaces.

Installation

The easiest way to get started with Untrue is through a web app.

npm i untrue @untrue/web

Compatible with any build tool: Parcel, Vite, Webpack, etc.

Native app development available with Detonator.

Get started

You can add Untrue to any part of your page.

import $ from "untrue";

import { Tree } from "@untrue/web";

import App from "./App";

const tree = new Tree(document.body);

// $ is a shorthand to represent slots

tree.mount($(App));

In this case, we're adding Untrue to body.

More on App in the next section.

Basic features

Interactivity

A component state can change at any time and Untrue knows which nodes should be updated in the DOM.

import $, { Hook } from "untrue";

function App() {
  const [counter, updateCounter] = Hook.useState(0);

  const onIncrement = () => {
    updateCounter(counter + 1);
  };

  // regular arrays are used to return a list of slots

  // after the first click, counter is no longer 0 but 1

  return [
    $("span", counter),
    $("button", { onclick: onIncrement }, "increment"),
  ];
}

export default App;

The output HTML will be:

<span>0</span> <button>increment</button>

button will have an onclick listener attached to it.

span will be updated with the new counter every time button is clicked.

Modularity

Components can be classes or functions and are used to group multiple slots.

import $, { Hook, Props } from "untrue";

function App() {
  return [
    $(Header, { title: "Untrue" }), // pass title as prop (external data)
    $(Footer, { year: 2049 }), // pass year as prop (external data)
  ];
}

interface HeaderProps extends Props {
  title: string;
}

function Header({ title }: HeaderProps) {
  const [counter, updateCounter] = Hook.useState(0); // internal data

  const onIncrement = () => {
    updateCounter(counter + 1);
  };

  return $("header", [
    $("h1", title),
    $("div", [
      $("span", counter),
      $("button", { onclick: onIncrement }, "increment"),
    ]),
  ]);
}

interface FooterProps extends Props {
  year: number;
}

function Footer({ year }: FooterProps) {
  return $("footer", [
    $("span", `copyright, ${year}`),
    $("br"),
    $("a", { href: "https://example.com" }, "some anchor link"),
  ]);
}

export default App;

The output HTML will be:

<header>
  <h1>Untrue</h1>
  <div>
    <span>0</span>
    <button>increment</button>
  </div>
</header>
<footer>
  <span>copyright, 2049</span>
  <br />
  <a href="https://example.com">some anchor link</a>
</footer>

Header has some counter that will be updated with button.

Lifecycle events

• mount: The first render.
• update: Every render after the first one.
• render: Every render. It's fired after mount or update events.
• unmount: Component has been unmounted.

Multiple event listeners can be attached to a single event. Specially useful to have more organized code.

import $, { Hook } from "untrue";

function App() {
  const [running, updateRunning] = Hook.useState(false);

  const onClick = () => {
    updateRunning(!running);
  };

  return [
    $("button", { onclick: onClick }, running ? "end timer" : "start timer"),
    $("br"),
    running ? $(Timer) : null,
  ];
}

function Timer() {
  const [counter, updateCounter] = Hook.useState(0);

  Hook.useMountLifecycle(() => {
    console.log("Timer mounted");
  });

  Hook.useUpdateLifecycle(() => {
    console.log("Timer updated");
  });

  Hook.useEffect(() => {
    const timeout = setTimeout(() => {
      updateCounter(counter + 1);
    }, 1000);

    return () => {
      clearTimeout(timeout);
    };
  }, [counter]);

  return $("span", counter);
}

export default App;

After the button click, the output HTML will be:

<button>end timer</button>
<br />
<span>0</span>

counter is incremented every second.

Timer mounted is logged first followed by Timer updated for updates.