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78 lines
2.6 KiB
Markdown
78 lines
2.6 KiB
Markdown
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# Astro Lit Renderer
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This is a plugin for [Astro](https://astro.build/) apps that enables server-side rendering of custom elements build with [Lit](https://lit.dev/).
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Server-side rendering uses [Declarative Shadow DOM](https://web.dev/declarative-shadow-dom/), a new web technology that allows custom elements to be rendered to HTML with __0 JavaScript__.
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## Installation
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Install `@astrojs/renderer-lit` and then add it to your `astro.config.mjs` in the `renderers` property:
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```
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npm install @astrojs/renderer-lit
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```
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__astro.config.mjs__
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```js
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export default {
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// ...
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renderers: [
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// ...
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'@astrojs/renderer-lit'
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]
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}
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```
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## Usage
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If you're familiar with Astro then you already know that you can import components into your templates and use them. What's different about custom elements is you can use the *tag name* directly.
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Astro needs to know which tag is associated with which component script. We expose this through exporting a `tagName` variable from the component script. It looks like this:
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__src/components/my-element.js__
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```js
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import { LitElement, html } from 'lit';
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export const tagName = 'my-counter';
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class Counter extends LitElement {
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}
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customElements.define(tagName, Counter);
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```
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> Note that exporting the `tagName` is __required__ if you want to use the tag name in your templates. Otherwise you can export and use the constructor, like with non custom element frameworks.
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In your Astro template import this component as a side-effect and use the element.
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__src/pages/index.astro__
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```jsx
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---
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import '../components/my-element.js';
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---
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<my-element></my-element>
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```
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> Note that Lit requires browser globals such as `HTMLElement` and `customElements` to be present. For this reason the Lit renderer shims the server with these globals so Lit can run. You *might* run into libraries that work incorrectly because of this.
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### Polyfills & Hydration
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The renderer automatically handles adding appropriate polyfills for support in browsers that don't have Declarative Shadow DOM. The polyfill is about *1.5kB*. If the browser does support Declarative Shadow DOM then less than 250 bytes are loaded (to feature detect support).
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Hydration is also handled automatically. You can use the same hydration directives such as `client:load`, `client:idle` and `client:visible` as you can with other libraries that Astro supports.
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```jsx
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---
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import '../components/my-element.js';
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---
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<my-element client:visible />
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```
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The above will only load the element's JavaScript when the user has scrolled it into view. Since it is server rendered they will not see any jank; it will load and hydrate transparently.
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