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Ity

A tiny dependency-free reactive app kernel for small browser apps, embeddable widgets, and progressive SPAs.

Ity 2 keeps the original Ity goal: do useful client-side app work without a framework stack, runtime dependencies, or a large bundle. The primary API is now reactive and platform-native: signals, computed values, effects, tagged HTML templates, Web Components, and a modern router. The original MVC classes are still included as a compatibility layer.

Why Ity 2?

  • Tiny runtime, no production dependencies.
  • Fine-grained reactive state with signal, computed, effect, and store.
  • Safe-by-default DOM templates: dynamic values become text unless explicitly marked with unsafeHTML.
  • Native Web Component support via component().
  • SPA routing with URLPattern support when available and a regex fallback when it is not.
  • Static/SSR string output through renderToString.
  • Optional View Transition integration for same-document route/render updates.
  • V1-compatible Model, Collection, View, Application, and SelectorObject.

Installation

npm install ity
import Ity, { signal, computed, html, render } from "ity";

The package ships ESM, CommonJS, browser IIFE, minified IIFE, source maps, and TypeScript declarations.

Quick Start

import { signal, computed, html, render } from "ity";

const count = signal(0);
const doubled = computed(() => count() * 2);

render(() => html`
  <button @click=${() => count.update((n) => n + 1)}>
    Count: ${count}
  </button>
  <p>Doubled: ${doubled}</p>
`, "#app");

When count changes, only the reactive render effect reruns. Dynamic text is inserted as text, not parsed as HTML.

Signals

Signals are callable values.

const name = Ity.signal("Ada");

name();               // "Ada"
name.set("Grace");    // "Grace"
name("Hedy");         // callable setter
name.update((v) => v.toUpperCase());
name.peek();          // read without dependency tracking

computed

const first = Ity.signal("Ada");
const last = Ity.signal("Lovelace");
const full = Ity.computed(() => `${first()} ${last()}`);

full(); // "Ada Lovelace"

Computed values are lazy and cached. They invalidate when dependencies change.

effect

const stop = Ity.effect((onCleanup) => {
  const controller = new AbortController();
  onCleanup(() => controller.abort());

  console.log("Current value", full());
});

stop();

batch and untrack

Ity.batch(() => {
  first.set("Grace");
  last.set("Hopper");
});

const snapshot = Ity.untrack(() => full());

batch coalesces dependent effects. untrack reads without subscribing the current computation.

store

const state = Ity.store({ name: "Ada", count: 1 });

state.name; // reactive read
state.count = 2;
state.$patch({ name: "Grace" });
state.$snapshot(); // plain object

const unsubscribe = state.$subscribe((value) => {
  console.log(value);
}, { immediate: true });

HTML Templates

html creates a template result. Use render to mount it.

const title = Ity.signal("Dashboard");

Ity.render(() => Ity.html`
  <section class=${["panel", "primary"]}>
    <h1>${title}</h1>
    <input .value=${title}>
    <button ?disabled=${false} @click=${() => title.set("Updated")}>
      Rename
    </button>
  </section>
`, "#app");

Supported bindings:

  • Text/content: ${value}.
  • Events: @click=${handler} or @click=${[handler, options]}.
  • Properties: .value=${value}.
  • Boolean attributes: ?disabled=${condition}.
  • Attributes: href=${url}, class=${["a", "b"]}, class=${{ active: true }}.
  • Style objects: style=${{ color: "red" }}.
  • Nested templates, DOM nodes, arrays, and signals.

Unsafe HTML

Dynamic values are safe text by default. If you intentionally want to parse a string as HTML, mark that boundary explicitly:

Ity.html`<article>${Ity.unsafeHTML(trustedHtmlString)}</article>`;

Only pass trusted content to unsafeHTML.

Render Options

const stop = Ity.render(view, "#app", {
  reactive: true,
  transition: true,
});

stop();

transition: true uses document.startViewTransition() when the browser supports it and falls back to a normal render otherwise.

Static and SSR Output

const markup = Ity.renderToString(() => Ity.html`
  <article>
    <h1>${title}</h1>
    ${Ity.unsafeHTML(trustedBodyHtml)}
  </article>
`);

renderToString escapes dynamic text and attributes, skips event/property bindings that only make sense in the browser, preserves boolean attributes, and keeps unsafeHTML explicit.

Components

component() defines a custom element and renders it with Ity templates.

Ity.component("ity-counter", {
  attrs: ["label"],
  shadow: true,
  styles: `
    button {
      border: 0;
      border-radius: 999px;
      padding: 0.65rem 1rem;
    }
  `,
  setup(ctx) {
    const label = ctx.attr("label");
    const count = Ity.signal(0);

    return () => Ity.html`
      <button @click=${() => count.update((n) => n + 1)}>
        ${label}: ${count}
      </button>
    `;
  }
});

Component context:

  • ctx.host: the custom element instance.
  • ctx.root: the shadow root or host render root.
  • ctx.attr(name): a signal for an observed attribute.
  • ctx.emit(name, detail, options): dispatch a composed bubbling custom event.
  • ctx.effect(fn): an effect that is disposed on disconnect.
  • ctx.onConnected(fn) and ctx.onDisconnected(fn): lifecycle hooks.

If a tag has already been defined, component() returns the existing constructor instead of throwing.

Router

const router = new Ity.Router({ transition: true });

router.add("/users/:id", (params, ctx) => {
  console.log(params.id, ctx.query, ctx.hash);
});

router.add("/files/*", (params) => {
  console.log(params.wildcard);
});

router.navigate("/users/42?tab=profile#panel=activity");

The router:

  • Uses native URLPattern when available.
  • Falls back to a small internal matcher for :param and * segments.
  • Parses query and hash params.
  • Exposes router.current as a signal.
  • Handles same-origin links matching a[data-ity-link].
  • Intercepts same-origin Navigation API events when the API is available.
  • Supports navigate(path, { replace, transition }).
  • Supports start() and stop().

For very small apps, use the convenience helper:

Ity.route("/settings", () => {
  Ity.render(Ity.html`<settings-page></settings-page>`, "#app");
});

V1 Compatibility

The original MVC API remains available:

const app = new Ity.Application();
const model = new Ity.Model({ data: { message: "Hello" } });

const view = new Ity.View({
  el: "#app",
  app,
  model,
  events: {
    "button": { click: "onClick" }
  },
  initialize() {
    this.model.on("change", this.render, this);
  },
  render() {
    this.select(".message").html(this.model.get("message"));
  },
  onClick() {
    this.model.set("message", "Updated");
  }
});

Compatibility classes:

  • Application: view registry and app-level event fan-out.
  • Model: data object, get, set, unSet, clear, events, sync.
  • Collection: model array, filtering, lookup, fetch, collection signal.
  • View: scoped element, delegated DOM events, event emitter, renderWith.
  • SelectorObject: jQuery-like scoped DOM traversal and mutation.

V1 models and collections also expose reactive state signals, so old and new code can be migrated incrementally.

SelectorObject

const view = new Ity.View({ el: ".parent" });

view
  .select(".item")
  .addClass("active")
  .attr("aria-current", true)
  .text("Selected")
  .parent()
  .find(".remove")
  .remove();

Supported methods include find, filter, first, last, parent, children, remove, before, after, append, prepend, html, empty, attr, text, on, off, addClass, removeClass, toggleClass, hasClass, and toArray.

Build

npm install
npm run build

This creates:

  • dist/ity.js
  • dist/ity.min.js
  • dist/ity.esm.js
  • dist/ity.esm.mjs
  • dist/ity.cjs.js
  • dist/ity.d.ts
  • Source maps

Test

npm test
npm run test:dist
npm run coverage

The suite covers the V2 reactive runtime, DOM templating, components, router, platform fallbacks, and V1 compatibility.

Browser Support

Ity 2 is built on standard browser APIs:

  • Custom Elements and Shadow DOM for components.
  • URLPattern when available, with an internal fallback.
  • document.startViewTransition() when available, with normal rendering as the fallback.
  • No dependency on the HTML Sanitizer API because it is not universally available. Ity keeps dynamic template values safe by using text nodes unless unsafeHTML is explicitly requested.

License

The MIT License (MIT)

Copyright (c) 2026 Dominic Cocchiarella

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.