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 (5 kB minimized; 1.61 kB with Brotli compression)
• 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 v3.0.0) (Read more about defer-hydration at zachleat.com)
• Experimental: Image Loading
• Experimental: Using import maps to simplify import URLs. This is for-future-reference when browser support broadens.

Integrations in the wild:

• Eleventy
• WebC
• Slinkity
• SvelteKit
• Bridgetown
• Lit

npm install @11ty/is-land

Add is-land.js to your primary bundle. It can be deferred and/or loaded asynchronously.

When using with web components it must be the first custom element defined (via customElements.define) on the page. Choose your style:

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

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

The framework autoinit examples shown below now require a separate is-land-autoinit.js file too.

<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:

• on:visible
• on:idle
• on:interaction (defaults to touchstart,click)
  • Change events with on:interaction="mouseenter,focusin"
• on:media
  • Viewport size: on:media="(min-width: 64em)"
  • Reduced motion:
    • Opt-in with on:media="(prefers-reduced-motion)"
    • Opt-out with on:media="(prefers-reduced-motion: no-preference)"
• Save Data (read about Save Data on MDN)
  • Opt-in with on:save-data
  • Opt-out with 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>

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

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)

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>

Demos and source in the HTML are available for each framework listed here. These examples require the is-land-autoinit.js JavaScript file (in addition to is-land.js).

Use the autoinit and import attributes together to import a third party library (or component code). autoinit can be one of petite-vue, vue, preact, or svelte. It is recommended to use a self-hosted framework library (future Eleventy integrations will automate this for you).

<is-land on:visible autoinit="petite-vue" import="https://unpkg.com/[email protected]/dist/petite-vue.es.js" v-scope="{ name: 'post-JS' }">
  Hello from <span v-html="name">pre-JS</span>
</is-land>

<!-- when import maps support is better, this simplifies with an entry for petite-vue in your import map -->
<is-land on:visible import="petite-vue" v-scope="{ name: 'post-JS' }">
  Hello from <span v-html="name">pre-JS</span>
</is-land>

• Small library (8K)
• Rendering modes: Client
• Progressive-enhancement friendly (full control of fallback content)
• Support for autoinit

<is-land on:visible autoinit="petite-vue" import="https://unpkg.com/[email protected]/dist/petite-vue.es.js" v-scope="{ name: 'post-JS' }">
  Hello from <span v-html="name">pre-JS</span>
</is-land>

• Larger library (51 kB)
• Rendering modes: Client-only, Server-only, Server + Client (Hydration)
• Support for autoinit

<is-land on:visible>
  <div id="vue-app">
    Hello from <span v-html="name">pre-JS</span>
  </div>

  <template data-island>
    <script type="module">
    import { createApp } from "https://unpkg.com/[email protected]/dist/vue.esm-browser.prod.js";

    createApp({
      data: () => ({ name: "post-JS" })
    }).mount("#vue-app")
    </script>
  </template>
</is-land>

• Smaller library (12 kB)
• Rendering modes: Client-only, Server-only, Server + Client (Hydration)
  • Requires a compiler for both client and server modes (tighter server coupling)
• Support for autoinit

This example uses an Eleventy/Svelte integration to compile a Svelte component.

{% assign component = "./lib/svelte/my-component.svelte" | svelte %}
<is-land on:visible autoinit="svelte" import="{{ component.clientJsUrl }}"></is-land>

<script>
  // using export to allow overrides via props
  export let name = 'world';

  let count = 0;

  function handleClick() {
    count += 1;
  }
</script>

<style>
  h1 { color: red }
</style>

<h1>Hello {name}</h1>

<button on:click={handleClick}>
  Clicked {count} {count === 1 ? 'time' : 'times'}
</button>

• Very small library (~5 kB)
• Rendering modes: Client-only, Server-only, Server + Client (Hydration)
• Support for autoinit

This example uses htm instead of JSX.

<is-land on:visible autoinit="preact" import="/lib/preact/preact-component.js"></is-land>

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);
}

• Small library (~7 kB)
• Rendering modes: Client-only, Server + Client (Hydration)
  • Note: Server-only is not supported: it requires Declarative Shadow DOM support to work without JS.
• No support for autoinit

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

import {html, css, LitElement} from "https://cdn.jsdelivr.net/gh/lit/dist@2/core/lit-core.min.js";

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

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

• Smaller library (15 kB)
• Rendering modes: Client-only
• No autoinit but it is not needed (functionality included for-free by Alpine.js)

<is-land on:visible import="https://unpkg.com/alpinejs">
  <div x-data="{ count: 0 }">
    Hello from Alpine.js!

    <button @click="count++">⬆️</button> <button @click="count--">⬇️</button> <span x-text="count"></span>
  </div>
</is-land>