Number of beers:

function plural(n) {

    let forms = ["bere", "beri", "de beri"];
    let index = n == 1 ? 0 : (n == 0 || (n % 100 > 0 && n % 100 < 20)) ? 1 : 2;
    let output = document.querySelector("#output");

    if (n.length > 0) {
        output.innerHTML = n + " " + forms[index];
    } else {
        output.innerHTML = "&nbsp;";
    }
}