load CDN libraries with fallback options

cdn_script_loader.js

/**
 *  Asynchronously loads a script
 *  A src with fallback/s, can be defined as an array of paths.
 *
 *  @param src {String|Array<String>} the script to load
 *  @param containerEl {HTMLElement} element to append script tag
 *  @return {Promise}
 */
const loadScript = ({ src, containerEl }) => {
    let srcs;
    if(Array.isArray(src)) {
        [srcs, src] = [src, src.shift()];
    }
    return new Promise((accept, reject) => {
        const script = document.createElement('script');
        script.addEventListener('load', () => accept(src));
        script.addEventListener('error', e => {
            if(srcs.length) {
                accept(this.loadScript({ src: srcs, containerEl }));
            }else {
                reject(e);
            }
        });
        script.src = src;
        script.async = true;
        containerEl.appendChild(script);
    });
};

const src = ['does-not-exist.js','https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.core.js'];

this.loadScript({ src , containerEl })
        .then(() => console.log('success'), (e) => console.log('problem with', this.interaction));