resize-observer-polyfill/src/ResizeObserverEntry.js

A polyfill for the Resize Observer API

import {createReadOnlyRect} from './utils/geometry.js';
import defineConfigurable from './utils/defineConfigurable.js';

export default class ResizeObserverEntry {
    /**
     * Element size of which has changed.
     * Spec: https://wicg.github.io/ResizeObserver/#dom-resizeobserverentry-target
     *
     * @readonly
     * @type {Element}
     */
    target;

    /**
     * Element's content rectangle.
     * Spec: https://wicg.github.io/ResizeObserver/#dom-resizeobserverentry-contentrect
     *
     * @readonly
     * @type {DOMRectReadOnly}
     */
    contentRect;

    /**
     * Creates an instance of ResizeObserverEntry.
     *
     * @param {Element} target - Element that is being observed.
     * @param {DOMRectInit} rectInit - Data of the element's content rectangle.
     */
    constructor(target, rectInit) {
        const contentRect = createReadOnlyRect(rectInit);

        // According to the specification following properties are not writable
        // and are also not enumerable in the native implementation.
        //
        // Property accessors are not being used as they'd require to define a
        // private WeakMap storage which may cause memory leaks in browsers that
        // don't support this type of collections.
        defineConfigurable(this, {target, contentRect});
    }
}