@lit/reactive-element/node/development/decorators/query-async.js

A simple low level base class for creating fast, lightweight web components

import { desc } from './base.js';

/**
 * @license
 * Copyright 2017 Google LLC
 * SPDX-License-Identifier: BSD-3-Clause
 */
// Note, in the future, we may extend this decorator to support the use case
// where the queried element may need to do work to become ready to interact
// with (e.g. load some implementation code). If so, we might elect to
// add a second argument defining a function that can be run to make the
// queried element loaded/updated/ready.
/**
 * A property decorator that converts a class property into a getter that
 * returns a promise that resolves to the result of a querySelector on the
 * element's renderRoot done after the element's `updateComplete` promise
 * resolves. When the queried property may change with element state, this
 * decorator can be used instead of requiring users to await the
 * `updateComplete` before accessing the property.
 *
 * @param selector A DOMString containing one or more selectors to match.
 *
 * See: https://developer.mozilla.org/en-US/docs/Web/API/Document/querySelector
 *
 * ```ts
 * class MyElement {
 *   @queryAsync('#first')
 *   first: Promise<HTMLDivElement>;
 *
 *   render() {
 *     return html`
 *       <div id="first"></div>
 *       <div id="second"></div>
 *     `;
 *   }
 * }
 *
 * // external usage
 * async doSomethingWithFirst() {
 *  (await aMyElement.first).doSomething();
 * }
 * ```
 * @category Decorator
 */
function queryAsync(selector) {
    return ((obj, name) => {
        return desc(obj, name, {
            async get() {
                await this.updateComplete;
                return this.renderRoot?.querySelector(selector) ?? null;
            },
        });
    });
}

export { queryAsync };
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