92 lines
3.1 KiB
Markdown
92 lines
3.1 KiB
Markdown
# ReactiveElement 1.0
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[](https://github.com/lit/lit/actions?query=workflow%3ATests)
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[](https://www.npmjs.com/package/@lit/reactive-element)
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[](https://lit.dev/discord/)
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[](https://github.com/web-padawan/awesome-lit)
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# ReactiveElement
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A simple low level base class for creating fast, lightweight web components.
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## About this release
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This is a stable release of `@lit/reactive-element` 1.0.0 (part of the Lit 2.0 release). If upgrading from previous versions of `UpdatingElement`, please see the [Upgrade Guide](https://lit.dev/docs/releases/upgrade/).
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## Documentation
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Full documentation is available at [lit.dev](https://lit.dev/docs/api/ReactiveElement/).
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## Overview
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`ReactiveElement` is a base class for writing web components that react to changes in properties and attributes. `ReactiveElement` adds reactive properties and a batching, asynchronous update lifecycle to the standard web component APIs. Subclasses can respond to changes and update the DOM to reflect the element state.
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`ReactiveElement` doesn't include a DOM template system, but can easily be extended to add one by overriding the `update()` method to call the template library. `LitElement` is such an extension that adds `lit-html` templating.
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## Example
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```ts
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import {
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ReactiveElement,
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html,
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css,
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customElement,
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property,
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PropertyValues,
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} from '@lit/reactive-element';
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// This decorator defines the element.
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@customElement('my-element')
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export class MyElement extends ReactiveElement {
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// This decorator creates a property accessor that triggers rendering and
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// an observed attribute.
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@property()
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mood = 'great';
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static styles = css`
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span {
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color: green;
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}
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`;
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contentEl?: HTMLSpanElement;
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// One time setup of shadowRoot content.
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createRenderRoot() {
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const shadowRoot = super.createRenderRoot();
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shadowRoot.innerHTML = `Web Components are <span></span>!`;
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this.contentEl = shadowRoot.firstElementChild;
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return shadowRoot;
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}
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// Use a DOM rendering library of your choice or manually update the DOM.
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update(changedProperties: PropertyValues) {
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super.update(changedProperties);
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this.contentEl.textContent = this.mood;
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}
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}
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```
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```html
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<my-element mood="awesome"></my-element>
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```
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Note, this example uses decorators to create properties. Decorators are a proposed
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standard currently available in [TypeScript](https://www.typescriptlang.org/) or [Babel](https://babeljs.io/docs/en/babel-plugin-proposal-decorators). ReactiveElement also supports a [vanilla JavaScript method](https://lit.dev/docs/components/properties/#declaring-properties-in-a-static-properties-field) of declaring reactive properties.
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## Installation
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```bash
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$ npm install @lit/reactive-element
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```
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Or use from `lit`:
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```bash
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$ npm install lit
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```
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## Contributing
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Please see [CONTRIBUTING.md](../../CONTRIBUTING.md).
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