ιota JS

ιota is a tiny UI library for JS. Its one and only focus is bundle size.

How small is small? 1.58kb min, 839b min+gzip, 760b min+brotli (bundlejs, 1.1.1). Woah.

It has a basic reactivity system (no batching etc.), and uses template strings to build UIs.

Should you use this for your app? Almost certainly no. Solid, Vue, Svelte, ArrowJS, Alpine, petite-vue.

When should you use this? In the specific case that you want to render your app from Javascript (if you're looking to spice up HTML, try alpine or petite-vue!), and bundle size is the thing that matters most.

You are likely to achieve smaller size than naive Vanilla JS, however if you were to abandon reactivity, then your html implementation would become so trivial that you could DIY and beat this library by a wide margin - the benefit of ιota is that non-reactive UI results in often disgustingly bad code.

Goals

• work predictably
• be very small
• have enough better than vanilla JS DX to justify using

Non-goals

• highly flexible / controllable reactivity
• JSX
• fancier templating arrowjs-style (templating into events and attrs)

Usage: reactivity

sig: Signals

Import sig from ιota to create a signal: const mySig = sig(0);

You can access the value of the signal by calling it: mySig(), or update the value of it by passing a value: mySig(1).

Note that you can pass mySig(undefined) and all will still set the signal as expected: choosing to set or not is based on the length of the arguments, not on the value of the first argument.

effect: Effects

To make things happen when the signal changes, you can use effect. When you access the contents of your signal in the effect, the effect will subscribe to that signal.:

const count = sig(0);
effect(() => console.log(count())); // log: 0
count(1); // log: 1

If you need to access a signal in an effect without creating a subscription, use untrack:

const count = sig(0);
effect(() => {
	const countValue = untrack(count);
	const doubleCount = untrack(() => count() * 2);
});

Derivations & Memos

And with just these three ingredients, we can build basically all reactive patterns!

If this was a heavier weight framework, things like microtask based or batched updates would be a thing, however, we are not. If you want performance first, go and use solid!

Derived values should just be functions:

const count = sig(0);
const doubleCount = () => count() * 2;

The final utility we export is useful if you have a very slow to calc reactive value and want to cache the value: memo. In most cases memo is likely to slow you down though, and if nothing else, its extra bundle size.

Usage: UI

html: Templating

ιota also provides minimal tools for building user interfaces: the html, ev, and attrs functions.

You can create a basic template using html:

const myElem = html`<div style="width: 1rem"><img src="cat.gif" /></div>`;
document.body.append(myElem);

You may template static values into your HTML, *BE VERY CAREFUL!: ιota supports templating in entire DOM nodes, but not attributes (see attrs)!:

// all will go well:
const expectedUI = html`<div>
	${1 + 3}
	${"woah!".toUpperCase()}
	${document.createElement("button")}
	${showButton
		? html`<button />`
		: null}
</div>`;

// this should not be expected to throw, however your output is likely to be garbled or unusable
const brokenUI = html`<img alt="a cool img" src="${myImg}" />`;

You may template in the following types:

• strings
• numbers (auto-converted to strings)
• DOM Nodes
• arrays of these types
• null & undefined

You should only use one top-level node in your template. The html function only returns the first node at the top level, so make sure to manually use an array of templates instead.

const justTheButton = html`<button />
	<div>I get entirely dropped!</div>`;

Reactivity

The key reason to use html, however, is that it supports reactivity.

ιota makes the disctinction between static and reactive values in templates very clear: if its a function, its reactive (remember that signals are functions!).

You can template in a function that returns any templatable value, like this:

const count = sig(0);
const ui = html`<div>
	The count is ${count} <br />
	Doubled, that's ${() => count() * 2}
</div>`;

attrs: Applying attributes

Before you mentally go "ew, why is this like this" at attrs and ev, remember that this framework is optimized for bundle size. These being separate, at the expense of comfort, allows the templating implementation (and therefore the bundle size) to be much smaller. Keep in mind that this framework is not intended for applications, its for applications where size matters primarily.

attrs is a utility that allows you to assign attributes to elements (reasonably) cleanly in your template:

// image from before:
const myImage = attr(html`<img alt="a cool img" />`, "src", myImg);

// use it in a template:
const myUi = html`
	<div id="image-wrap">${attrs(html`<img alt="a cool img" />`, "src", myImg)}</div>
`;

attrs can apply multiple attributes in a single call: attrs(myimg, "src", catImageSrc, "alt", catImageAlt);

attrs is also reactive: you can provide a signal / function returning a string:

const width = sig(500);
const resizableDiv = attrs(html`<div />`, "style", () => `width: ${width()}px`);

ev: Event handling

Introducing attrs' close cousin: ev, which adds event handlers to an element.:

const count = sig(0);
const ui = ev(html`<button>I have been clicked ${count} times</button>`, "click", () =>
	count(count() + 1)
);

Components

Use a function:

const MyBtn = (content, onClick) =>
	ev(html`<button class="my-btn">${content}</button>`, "click", onClick);

const count = sig(0);
const ui = html` <div>
	<h1>My Cool app</h1>
	${MyBtn("say hi!", () => alert("hi there!"))}
	<br />
	${MyBtn(
		() => `a count of ${count()}`,
		() => count(count() + 1)
	)}
</div>`;

Loops

Use a nested template:

html`
	<div>
		${names.map((n) =>
			ev(html`<button>Say hi to ${n}!</button>`, "click", () => alert(`hi ${n}!`))
		)}
	</div>
`;

Shoutouts

• ArrowJS - the inspiration of this library. If you want something like ιota but a lil bigger and with better DX, try Arrow! It's cool!
• Solid - inspired the use of signals. If you want to build a full app or website, this is 100% my best recommendation. It just rocks!
• You! - thanks for using my software. If you notice a bug, or want an extra feature that doesn't fall under the non-goals, feel free to open an issue or PR :) If you particularly like this or, any other of my software, feel free to buy me a coffee ;)