Dynamic import function for ES modules polyfill

dynamic-module-import-polyfill.js

// Addapted from  :
// https://github.com/tc39/proposal-dynamic-import

function importModule(url) {
    return new Promise((resolve, reject) => {
        const script = document.createElement("script");
        const loaderId = "__tempModuleLoadingVariable" + Math.random().toString(32).substring(2);

        window[loaderId] = function( m ){
            resolve( m );
            delete window[loaderId];
            script.remove();
        };

        script.onerror = () => {
            reject(new Error("Failed to load module script with URL " + url));
            delete window[loaderId];
            script.remove();
        }; 
        script.type = "module";
        script.textContent = `import * as m from "${url}"; window.${loaderId}( m.default )`;

        document.documentElement.appendChild(script);
    });
}