jitsi-meet/react/features/base/participants/preloadImage.web.js

// @flow

import { isIconUrl } from './functions';

/**
 * Tries to preload an image.
 *
 * @param {string | Object} src - Source of the avatar.
 * @param {boolean} useCORS - Whether to use CORS or not.
 * @param {boolean} tryOnce - If true we try to load the image only using the specified CORS mode. Otherwise both modes
 * (CORS and no CORS) will be used to load the image if the first attempt fails.
 * @returns {Promise}
 */
export function preloadImage(
        src: string | Object,
        useCORS: ?boolean = false,
        tryOnce: ?boolean = false
): Promise<Object> {
    if (isIconUrl(src)) {
        return Promise.resolve({ src });
    }

    return new Promise((resolve, reject) => {
        const image = document.createElement('img');

        if (useCORS) {
            image.setAttribute('crossOrigin', '');
        }
        image.onload = () => resolve({
            src,
            isUsingCORS: useCORS
        });
        image.onerror = error => {
            if (tryOnce) {
                reject(error);
            } else {
                preloadImage(src, !useCORS, true)
                    .then(resolve)
                    .catch(reject);
            }
        };

        // $FlowExpectedError
        image.referrerPolicy = 'no-referrer';
        image.src = src;
    });
}