JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li tabindex="0">a</li>
    <li tabindex="0">a</li>
    <li tabindex="0">a</li>
    <li tabindex="0">a</li>
</ul>

JavaScript

window.onkeydown = function(e) {
    e = e || event;
    switch (e.keyCode) {
        case 37: alert('left');
        case 38: alert('up'); 
            // http://stackoverflow.com/a/7208662/1156119
            break;
        case 39: alert('right'); 
        case 40: alert('down');
            // http://stackoverflow.com/a/7208662/1156119
            break;
    }
}