express-param.html

<script>
    class ExpressParam extends HTMLElement {
        constructor() {
            super();

            this.name = null;
            this.callback = null;
        }

        static get observedAttributes() {
            return [
                'name'
            ];
        }

        attributeChangedCallback(name, oldValue, newValue) {
            switch (name) {
                case 'name': {
                    this.name = newValue;
                    break;
                }
            }
        }

        expressReadyCallback(app, express, router, route) {
            if (router) {
                prepareWithRouter(this, router);
            }
            else {
                prepareWithApp(this, app);
            }

            function prepareWithRouter(context, router) {

                if (!context.name) {
                    console.log('using router.param() without specifying a name is deprecated as of Express v4.11.0');
                }

                if (Array.isArray(context.name)) {
                    throw 'ExpressParamError: router.param() does not accept an array of route parameters';
                }

                router.param(context.name, context.callback);
            }

            function prepareWithApp(context, app) {
                app.param(context.name, context.callback);
            }
        }
    }

    window.customElements.define('express-param', ExpressParam);
</script>