xnav.js

TagBuilder.withTagName("x-navigation")
    .withMarkup("<button id='nav_c64' data-target='c64'>C64</button><button id='atari5200' data-target='atari5200'>Atari 5200</button><button id='coleco-1p' data-target='coleco-1p'>Colecovision</button>")
    .withConnectedCallback(function () {
        DomQuery.querySelectorAll("x-navigation button").addEventListener("click", (evt) => {
            let target = evt.target.dataset["target"];
            location.href = target + '.html';
        }).each((item => {
            item.removeClass("hidden");
            if (item.attr("data-target").value == DomQuery.byId(this).attr("selected").value) {
                item.addClass("hidden");
            }
        }));
    })
    .register();

That is pretty gnarly, but you gotta do it.