A simple polyfill for the "jQuery style methods" that have been added recently. Written in ES6 syntax

polyfill.js

function polyfill(object, name, value) {

    if (typeof object[name] !== typeof value) {

        Object.defineProperty(object, name, {
            value,
            configurable: true,
            enumerable: false,
            writable: true
        });

    }

}

function polfillAll(objects, methods) {

    if (!Array.isArray(objects)) {
        objects = [objects];
    }

    objects.forEach((object) => {

        Object
            .entries(methods)
            .forEach(([key, value]) => polyfill(object, key, value));

    });

}

polyfill(
    Object,
    "entries",
    (object) => Object.keys(object).map((key) => [key, object[key]])
);

let addToFrag = (...args) => {

    let frag = document.createDocumentFragment();

    args.forEach((arg) => {

        frag.appendChild(
            arg instanceof Node
                ? arg
                : document.createTextNode(String(arg))
        );

    });

    return frag;

};

polyfillAll(
    [
        Element.prototype,
        Document.prototype,
        DocumentFragment.prototype
    ],
    {

        append(...args) {
            this.appendChild(addToFrag(...args));
        }

        prepend(...args) {
            this.insertBefore(addToFrag(...args), this.firstChild);
        }

    }
);

polyfill(Element.prototype, "closest", (selector) => {

    let element = this;
    let closest = null;

    if (document.documentElement.contains(element)) {

        do {

            if (element.matches(selector)) {

                closest = element;
                break;

            }

            element = element.parentElement || element.parentNode;

        } while (element !== null);

    }

    return closest;

});

polyfillAll(
    [
        Element.prototype,
        CharacterData.prototype,
        DocumentType.prototype
    ]
    {

        before(...args) {
            this.parentNode.insertBefore(addToFrag(...args), this);
        }

        after(...args) {
            this.parentNode.insertBefore(addToFrag(...args), this.nextSibling);
        }

        remove() {

            if (this.parentNode) {
                this.parentNode.removeChild(this);
            }

        }

        replaceWith(...args) {

            // I only THINK this is a complete polyfill. Kinda hard to follow
            // the MDN example.

            this.before(...args);
            this.remove();

        }

    }
);

// NodeList.prototype.forEach.length = 1
polyfill(NodeList.prototype, "forEach", (...args) => {
    Array.prototype.forEach.apply(this, args);
});

The polyfillAll methods (before, replaceWith etc.) should have a length of 0