<is-land>

A new performance-focused way to add interactive client-side components to your web site.

Or, more technically: a framework independent partial hydration islands architecture implementation.

• View the demos
• Check out the initial screencast on Eleventy’s YouTube channel and the follow up screencast with more framework examples.
• Learn more about Islands Architecture

Features:

• Easy to add to existing components
• Zero dependencies
• Not tightly coupled to a server framework or site generator tool.
• Small footprint (1.79 kB compressed)
• Server-rendered (SSR) component examples available for SSR-friendly frameworks (Lit, Svelte, Vue, Preact are provided)

Examples for:

• Web Components
• Web Components using Declarative Shadow DOM (New in v3.0.0)
• Svelte (and SSR)
• Vue (and petite-vue) (and SSR)
• Preact (and SSR)
• Lit (and SSR)
• Alpine.js
• Embedded in Markdown
• defer-hydration Component Attribute Support (New in v3) (Read more about defer-hydration at zachleat.com)
• Using import maps to simplify import URLs.
• Renaming <is-land> tag name or the on: attribute prefix
• Experimental: Image Loading
• Stress test of 10000 islands
• Complex nested is-land test

Integrations in the wild: Eleventy, WebC, Slinkity, SvelteKit, Bridgetown, Lit

Installation

Available on npm at @11ty/is-land.

npm install @11ty/is-land

<script type="module" src="/is-land.js"></script>

Add is-land.js to your primary bundle.

It can be deferred and/or loaded asynchronously. When using with web components it must be loaded before any other custom elements (via customElements.define) on the page. Choose your style:

Usage

<is-land>This is an island.</is-land>

Add any number of loading conditions to this tag to control how and when the island is initialized. You can mix and match. All conditions be satisfied to initialize.

• on:visible
• on:load (new in v5)
• on:idle
• on:interaction (defaults to touchstart,click)
  • Change events with on:interaction="mouseenter,focusin"
• on:media
  • When Viewport size matches: on:media="(min-width: 64em)"
  • Reduced motion:
    • When user prefers reduced motion on:media="(prefers-reduced-motion)"
    • When user has no preference on motion on:media="(prefers-reduced-motion: no-preference)"
• Save Data (read about Save Data on MDN)
  • When Save Data is active on:save-data
  • When Save Data is inactive on:save-data="false"

<is-land on:visible on:idle>
  <!-- your HTML here -->

  <is-land on:media="(min-width: 64em)">
    <!-- Islands can be nested -->
    <!-- Islands inherit all of their parents’ loading conditions -->
  </is-land>
</is-land>

Controlling Fallback Content

Pre-JS

<is-land on:visible on:idle>
  <vanilla-web-component>
    Put your pre-JS fallback content in your web component.
  </vanilla-web-component>
</is-land>

Post-JS with <template>

Place any post-JS content inside of one or more <template data-island> elements anywhere in the <is-land>. These will be swapped with their template content. You can nest an <is-land> in there if you want!

<is-land on:visible on:idle>
  <template data-island>
    <vanilla-web-component>
      This component is post-JS.
    </vanilla-web-component>
  </template>
</is-land>

• Use data-island="replace" to replace the contents of the <is-land> with the template.
• Use data-island="once" to run a template’s contents once per page (keyed from template contents). (New in v2.0.1)

Run your own custom JavaScript, load your own CSS

Embed a script inside the template to run custom JS when the island’s loading conditions have been satisfied!

<is-land on:visible>
  <template data-island>
    <!-- CSS -->
    <style>/* My custom CSS */</style>
    <link rel="stylesheet" href="my-css-file.css">

    <!-- JS -->
    <script type="module">console.log("Hydrating!");</script>
    <script type="module" src="my-js-file.js"></script>
  </template>
</is-land>

You can also use the ready attribute for styling, added to the <is-land> when the island has been hydrated.

<style>
is-land[ready] {
  background-color: lightgreen;
}
</style>

Framework Component Support

• type: initialize a framework initialization type, registered by you. Examples included for: alpine, petite-vue, vue, vue-ssr, preact, preact-ssr, svelte, or svelte-ssr.

Demos, examples, and source code are available for each framework listed here.

Petite Vue

• Examples
• Small library (~9K)
• Rendering modes: Client
• Progressive-enhancement friendly (control fallback content)

<script type="module">
// Define once for any number of Petite Vue islands.
Island.addInitType("petite-vue", async (target) => {
	const { createApp } = await import("https://unpkg.com/[email protected]/dist/petite-vue.es.js");
	createApp().mount(target);
});
</script>
<is-land on:visible type="petite-vue" v-scope="{ name: 'Vue' }">
  Hello from <span v-html="name">HTML</span>
</is-land>

Vue

• Examples
• Larger library (~73 kB)
• Rendering modes: Client (shown), Server, Server + Client (Hydration)

<script type="module">
// Define once for any number of Vue islands.
Island.addInitType("vue", async (target) => {
	const { createApp } = await import("https://unpkg.com/[email protected]/dist/vue.esm-browser.js");
	createApp({
		data: () => (target.dataset), // use <is-land data-> attributes as component data
	}).mount(target);
});
</script>
<is-land on:visible type="vue" data-name="Vue">
	Hello from <span v-text="name"></span>
</is-land>

Svelte

• Examples (using Import Maps)
• Medium-sized library
• Rendering modes: Client, Server, Server + Client (Hydration)
• Requires a compiler for client mode (uncommon)

<script type="module">
// Define once for any number of Svelte islands.
Island.addInitType("svelte", async (target) => {
	// requires an Import map and svelte is lazy loaded when island is ready
	const { mount } = await import("svelte");
	const component = await import(target.getAttribute("import"));

	mount(component.default, {
		target: target,
		props: {},
	});
});
</script>
<!-- This example uses an Eleventy `svelte` Universal Filter (see SveltePlugin.cjs) -->
{% assign component = "./lib/svelte/my-component-js-only.svelte" | svelte %}
<is-land on:visible type="svelte" import="{{ component.clientJsUrl }}"></is-land>

Show sample Import Map

<!-- importmap from https://generator.jspm.io/ -->
<script type="importmap">
{
	"imports": {
		"svelte": "https://unpkg.com/[email protected]/src/index-client.js",
		"svelte/internal/client": "https://unpkg.com/[email protected]/src/internal/client/index.js",
		"svelte/internal/flags/legacy": "https://unpkg.com/[email protected]/src/internal/flags/legacy.js"
	},
	"scopes": {
		"https://unpkg.com/": {
			"clsx": "https://unpkg.com/[email protected]/dist/clsx.mjs",
			"esm-env": "https://unpkg.com/[email protected]/index.js",
			"esm-env/browser": "https://unpkg.com/[email protected]/true.js",
			"esm-env/development": "https://unpkg.com/[email protected]/false.js",
			"esm-env/node": "https://unpkg.com/[email protected]/false.js"
		}
	}
}
</script>

Preact

• Examples
• Small library (~9 kB)
• Rendering modes: Client (shown), Server, Server + Client (Hydration)
• No compiler needed when using htm rather than JSX.

<script type="module">
// Define once for any number of Preact islands.
Island.addInitType("preact", async (target) => {
	const component = await import(target.getAttribute("import"));
	component.default(target);
});
</script>
<is-land on:visible type="preact" import="preact-component.js"></is-land>

Example component code for preact-component.js:

import { html, render } from 'https://unpkg.com/htm/preact/index.mjs?module'

function App (props) {
  return html`<p><strong>Hello ${props.name}!</strong></p>`;
}

export default function(el) {
  render(html`<${App} name="from Preact" />`, el);
}

Lit

• Examples (using Import Maps)
• Small library (~10 kB)
• Rendering modes: Client, Server, Server + Client (Hydration)

<is-land on:visible import="lit-component.js">
  <lit-component name="Post-JS">Pre-JS Content</lit-web-component>
</is-land>

Show sample Import Map

<!-- importmap from https://generator.jspm.io/ -->
<script type="importmap">
{
	"imports": {
		"lit": "https://unpkg.com/[email protected]/index.js"
	},
	"scopes": {
		"https://unpkg.com/": {
			"@lit/reactive-element": "https://unpkg.com/@lit/[email protected]/reactive-element.js",
			"lit-element/lit-element.js": "https://unpkg.com/[email protected]/lit-element.js",
			"lit-html": "https://unpkg.com/[email protected]/lit-html.js",
			"lit-html/is-server.js": "https://unpkg.com/[email protected]/is-server.js"
		}
	}
}
</script>

Example component code lit-component.js:

import {html, css, LitElement} from "lit";

customElements.define('lit-component', class extends LitElement {
  static properties = {
    name: {type: String},
  };

  render() {
    return html`<p>Hello, ${this.name || "Stranger"}!</p>`;
  }
});

Alpine.js

• Examples
• Smaller library (~20 kB)
• Rendering modes: Client
• Progressive-enhancement friendly (control fallback content)

<script type="module">
// Define once for any number of Alpine islands.
Island.addInitType("alpine", async (target) => {
	await import("https://unpkg.com/[email protected]/dist/cdn.min.js");
});

// Workaround for Alpine global mount
Island.addFallback("[x-data]", (readyPromise, node) => {
  if(node.hasAttribute("x-ignore")) {
    return;
  }

  node.setAttribute("x-ignore", "");

  return readyPromise.then(() => {
    node.removeAttribute("x-ignore");

    if(Alpine) {
      Alpine.nextTick(() => Alpine.initTree(node));
    }
  });
});
</script>
<is-land on:visible type="alpine">
  <div x-data="{ name: 'Alpine.js' }">
    Hello from <span x-text="name">HTML</span>!
  </div>
</is-land>

Solid.js

• Examples (using Import Maps)
• Medium library (~40 kB)
• Rendering modes: Client