gistfile1.js

const weekday = {
    0: "Sunday",
    1: "Monday",
    2: "Tuesday",
    3: "Wednesday",
    4: "Thursday",
    5: "Friday",
    6: "Saturday",
}

function getToday() {
    const today = new Date();
    const todayString = `It's ${weekday[today.getDay()]}! It's ${today.getHours()}:${today.getMinutes()}:${today.getSeconds()}`;
    $('#currentTimeParagraph').text(todayString);
}

function daysLeft() {
    const today = new Date();

    const urlParams = new URLSearchParams(window.location.search);
    const targetYear = urlParams.get('targetYear') | today.getFullYear();

    const christmas = new Date();
    christmas.setDate(24);
    christmas.setMonth(11);

    const diff = christmas.getTime() - today.getTime();
    const yearDiff = targetYear - today.getFullYear()
    $('#christmasTime').text(`Days until Christmas: ${diff / (1000 * 60 * 60 * 24) + (365 * yearDiff)} days`);
}

$(document).ready(() => {
    daysLeft();
    getToday();
    setInterval(getToday, 1000);
});

// run `npx http-server` on your project folder
// open `localhost:8080` on browser
// try using a targetYear
// using url `localhost:8080?targetYear=2021`