more/webcomponents/minimal-es5-setup.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="utf-8">
    <title>Web components example</title>
</head>

<body>
    <script src="https://unpkg.com/es6-shim@0.35.5/es6-shim.min.js"></script>
    <script src="https://unpkg.com/@webcomponents/custom-elements"></script>
    <script>

        // Works in IE11+
        function LegacyElement() {
            return Reflect.construct(HTMLElement, [], this.constructor);
        }
        LegacyElement.prototype = Object.create(HTMLElement.prototype);
        LegacyElement.prototype.constructor = LegacyElement;
        LegacyElement.prototype.connectedCallback = function () {
            this.appendChild(document.createTextNode("A little rusty!"));
        };
        Object.setPrototypeOf(LegacyElement, HTMLElement);

        customElements.define("legacy-element", LegacyElement);

    </script>
    <script type="module">

        // Only for modern browsers
        customElements.define("modern-element", class extends HTMLElement {
            connectedCallback() {
                this.appendChild(document.createTextNode("Shiny!"));
            }
        });

    </script>
    <!-- Note that custom elements can not be self-closing -->
    <legacy-element></legacy-element>
    <modern-element></modern-element>
</body>

</html>