@lit/reactive-element
Advanced tools
Package description
The @lit/reactive-element package provides a base class for creating lightweight, reactive components. It is part of the Lit library, which is designed for building fast, lightweight web components. The reactive-element package focuses on the reactive system that powers Lit components, allowing developers to create and manage properties that automatically update the component when changed.
Reactive properties
This feature allows the creation of reactive properties that trigger updates to the component when their values change. The example defines a custom element with a reactive property 'name'. When 'name' changes, the 'updated' method logs the new value.
import { ReactiveElement } from '@lit/reactive-element';
class MyElement extends ReactiveElement {
static properties = {
name: {type: String}
};
constructor() {
super();
this.name = 'Lit';
}
updated(changedProperties) {
if (changedProperties.has('name')) {
console.log(`Name updated to: ${this.name}`);
}
}
}
customElements.define('my-element', MyElement);Lifecycle callbacks
Lifecycle callbacks provide hooks into the component's lifecycle. This example shows how to use 'connectedCallback' and 'disconnectedCallback' to perform actions when the element is added to or removed from the DOM.
import { ReactiveElement } from '@lit/reactive-element';
class MyElement extends ReactiveElement {
connectedCallback() {
super.connectedCallback();
console.log('Element added to the page.');
}
disconnectedCallback() {
super.disconnectedCallback();
console.log('Element removed from the page.');
}
}
customElements.define('my-element', MyElement);React is a popular library for building user interfaces. It uses a virtual DOM for efficient updates, similar to how @lit/reactive-element uses reactive properties to manage updates. However, React is generally used for larger applications and offers a more comprehensive ecosystem of tools and extensions.
Vue is another popular framework that provides reactive components. Like @lit/reactive-element, Vue components automatically update when reactive data changes. Vue offers a more integrated solution with built-in directives and a more opinionated structure, which differs from the minimalistic and low-level approach of @lit/reactive-element.
Readme
A simple low level base class for creating fast, lightweight web components.
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.
Full documentation is available at lit.dev.
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.
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.
import {
ReactiveElement,
html,
css,
customElement,
property,
PropertyValues,
} from '@lit/reactive-element';
// This decorator defines the element.
@customElement('my-element')
export class MyElement extends ReactiveElement {
// This decorator creates a property accessor that triggers rendering and
// an observed attribute.
@property()
mood = 'great';
static styles = css`
span {
color: green;
}
`;
contentEl?: HTMLSpanElement;
// One time setup of shadowRoot content.
createRenderRoot() {
const shadowRoot = super.createRenderRoot();
shadowRoot.innerHTML = `Web Components are <span></span>!`;
this.contentEl = shadowRoot.firstElementChild;
return shadowRoot;
}
// Use a DOM rendering library of your choice or manually update the DOM.
update(changedProperties: PropertyValues) {
super.update(changedProperties);
this.contentEl.textContent = this.mood;
}
}
<my-element mood="awesome"></my-element>
Note, this example uses decorators to create properties. Decorators are a proposed standard currently available in TypeScript or Babel. ReactiveElement also supports a vanilla JavaScript method of declaring reactive properties.
$ npm install @lit/reactive-element
Or use from lit:
$ npm install lit
Please see CONTRIBUTING.md.
FAQs
A simple low level base class for creating fast, lightweight web components
We found that @lit/reactive-element demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 9 open source maintainers collaborating on the project.
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