Load Polyfills based on Feature Detection

featureDetectionPolyfills.js

function browserSupportsAllFeatures() {
    // Your Polyfill needs go here
    return window.Promise && window.fetch && window.Symbol;
}

function loadScript(src, done) {
    let js = document.createElement('script');
    js.src = src;
    js.onload = function() {
        done();
    };
    js.onerror = function() {
        done(new Error('Failed to load script ' + src));
    };
    document.head.appendChild(js);
}

if (browserSupportsAllFeatures()) {
    // Browsers that support all features run `main()` immediately.
    main();
} else {
    // All other browsers loads polyfills and then run `main()`.
    loadScript('/path/to/polyfills.js', main);
}

function main(err) {
    if (err) { console.error('An error occurred loading the necessary scripts: %O', err);
    // Initiate all other code paths.
    // If there's an error loading the polyfills, handle that
    // case gracefully and track that the error occurred.
}