isolet Widget Isolation

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isolet-js packages any component (React, Solid, Svelte, vanilla JS, etc.) into a self-contained, isolated widget. Widgets render inside shadow DOM by default, so styles are fully scoped. Output formats include IIFE (script tag), ESM, and CommonJS.

Install

npm install isolet-js

Core API: `createIsolet`

import { createIsolet } from "isolet-js";

const widget = createIsolet({
  name: "my-widget",          // required: unique identifier
  mount: myMountFn,           // required: (container, props) => cleanup | void
  css: `h1 { color: red; }`,  // optional: scoped CSS
  isolation: "shadow-dom",    // "shadow-dom" | "scoped" | "none"
  shadowMode: "open",         // "open" | "closed"
  hostAttributes: { "data-widget": "true" },
  zIndex: 9999,
});

widget.mount(document.body, { title: "Hello" }); // mount into target
widget.update({ title: "Updated" });             // update props
widget.unmount();                                // tear down

// Instance properties
widget.container;   // HTMLElement — the render container
widget.shadowRoot;  // ShadowRoot | null
widget.mounted;     // boolean

Framework Adapters

React

import { createIsolet } from "isolet-js";
import { react } from "isolet-js/react";

function Greeting({ name }: { name: string }) {
  return <h1>Hello, {name}!</h1>;
}

const widget = createIsolet({
  name: "greeting",
  mount: react(Greeting),
  css: `h1 { color: tomato; font-family: sans-serif; }`,
});

widget.mount(document.body, { name: "World" });
widget.update({ name: "Isolet" });
widget.unmount();

Vanilla JS

import { createIsolet } from "isolet-js";
import { vanilla } from "isolet-js/vanilla";

const widget = createIsolet({
  name: "counter",
  mount: vanilla((container, props) => {
    let count = props.initial ?? 0;
    const btn = document.createElement("button");
    btn.textContent = `Count: ${count}`;
    btn.onclick = () => {
      btn.textContent = `Count: ${++count}`;
    };
    container.appendChild(btn);

    // Return cleanup function
    return () => container.removeChild(btn);
  }),
});

widget.mount(document.getElementById("app"), { initial: 5 });

Solid

import { createIsolet } from "isolet-js";
import { render } from "solid-js/web";
import App from "./App";

const widget = createIsolet({
  name: "solid-widget",
  mount(container, props) {
    const dispose = render(() => <App {...props} />, container);
    return dispose; // dispose is the cleanup function
  },
});

Svelte

import { createIsolet } from "isolet-js";
import App from "./App.svelte";

const widget = createIsolet({
  name: "svelte-widget",
  mount(container, props) {
    const app = new App({ target: container, props });
    return () => app.$destroy();
  },
});

Isolation Modes

// Full CSS isolation — shadow DOM (default)
createIsolet({ name: "w", mount: fn, isolation: "shadow-dom" });

// Scoped — plain div wrapper, styles injected globally
createIsolet({ name: "w", mount: fn, isolation: "scoped" });

// No isolation — mounts directly into target element
createIsolet({ name: "w", mount: fn, isolation: "none" });

CLI

npx isolet-js init            # scaffold isolet.config.ts
npx isolet-js build           # bundle widget(s) from config
npx isolet-js build --watch   # rebuild on file changes
npx isolet-js build --minify  # minified production build

Config File

// isolet.config.ts
import { defineConfig } from "isolet-js";

export default defineConfig({
  name: "my-widget",
  entry: "./src/index.ts",
  styles: "./src/widget.css",       // CSS to inline; url() assets become data URIs
  format: ["iife", "esm"],          // output formats
  outDir: "./dist",                 // default: "dist"
  globalName: "MyWidget",           // global name for IIFE builds
  external: ["react"],              // don't bundle these deps
  dts: true,                        // emit .d.ts files
  minify: true,                     // minify output
  platform: "browser",              // target platform
});

Multiple Widgets

export default defineConfig([
  { name: "widget-a", entry: "./src/a.ts", styles: "./src/a.css" },
  { name: "widget-b", entry: "./src/b.ts", format: ["esm"] },
]);

CSS & Asset Handling

The build pipeline handles everything automatically:

styles in config → CSS is read, url() references (fonts, images) inlined as data URIs, result available as __ISOLET_CSS__ in your entry
.css imports → converted to JS string exports (shadow DOM safe)
Asset imports (.png, .woff2, .mp3, etc.) → inlined as data URIs
styles: "./path.css" in createIsolet → resolved and inlined at build time

// Entry file using __ISOLET_CSS__ injected by CLI
import { createIsolet } from "isolet-js";
import { react } from "isolet-js/react";
import MyComponent from "./MyComponent";

declare const __ISOLET_CSS__: string;

export const widget = createIsolet({
  name: "my-widget",
  css: __ISOLET_CSS__,   // populated from config.styles at build time
  mount: react(MyComponent),
});

Or reference the CSS path directly (auto-resolved at build time):

createIsolet({
  name: "my-widget",
  styles: "./widget.css",  // isolet build resolves this
  mount: react(MyComponent),
});

Manual Vite Plugin Setup

If using Vite directly instead of the CLI:

// vite.config.ts
import { defineConfig } from "vite";
import {
  cssTextPlugin,
  inlineAssetsPlugin,
  autoStylesPlugin,
} from "isolet-js/plugins";

export default defineConfig({
  plugins: [cssTextPlugin(), inlineAssetsPlugin(), autoStylesPlugin()],
});

Script Tag (IIFE) Usage

<script src="https://unpkg.com/isolet-js/dist/index.iife.js"></script>
<script>
  const { createIsolet } = __ISOLET__;

  const widget = createIsolet({
    name: "inline-widget",
    mount(container, props) {
      container.innerHTML = `<p>Hello, ${props.name ?? "World"}!</p>`;
    },
    css: `p { font-family: sans-serif; color: navy; }`,
  });

  widget.mount(document.body, { name: "Visitor" });
</script>

For a bundled custom widget via IIFE:

// isolet.config.ts
export default defineConfig({
  name: "my-widget",
  entry: "./src/index.ts",
  format: ["iife"],
  globalName: "MyWidget",
  minify: true,
});

<!-- Resulting script tag distribution -->
<script src="./dist/my-widget.iife.js"></script>
<script>
  MyWidget.widget.mount(document.getElementById("root"), { title: "Hi" });
</script>

Common Patterns

Lazy-mount on demand

const widget = createIsolet({ name: "chat", mount: react(ChatApp), css: styles });

document.getElementById("open-chat").addEventListener("click", () => {
  if (!widget.mounted) {
    widget.mount(document.body, { userId: currentUserId });
  }
});

document.getElementById("close-chat").addEventListener("click", () => {
  widget.unmount();
});

z-index overlay widget

const modal = createIsolet({
  name: "modal",
  mount: react(ModalComponent),
  css: modalStyles,
  zIndex: 10000,
  hostAttributes: { role: "dialog", "aria-modal": "true" },
});

Reactive props updates

const widget = createIsolet({ name: "status", mount: react(StatusBar), css });
widget.mount(document.body, { status: "idle" });

// Later, update without remounting:
widget.update({ status: "loading" });
widget.update({ status: "done" });

Troubleshooting

Styles leaking in or out Use isolation: "shadow-dom" (default). Verify your css option or styles path is correctly set — without CSS in the shadow root, the host page styles will not apply inside.

__ISOLET_CSS__ is undefined This variable is only injected by the isolet build CLI when styles is set in config. For manual Vite builds, add autoStylesPlugin() to your Vite config.

Component not rendering Ensure the mount function appends to container, not to document.body. In shadow DOM mode, the container is inside the shadow root.

Cleanup not running Return a cleanup function from your mount callback. Without it, widget.unmount() cannot tear down framework internals (timers, subscriptions, etc.).

IIFE global not found Check globalName in config matches what you reference in HTML. The runtime core exposes globalThis.__ISOLET__ when no globalName is set.

External deps not found at runtime If you set external: ["react"], the host page must provide React globally or via module federation before your widget script loads.

isolet-widget-isolation