JSFiddle - React, Tailwind, and code Playground

by Brandon Trecki

HTML

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Calendar</title>

    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
    <!-- Bootstrap CSS -->
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css"
          integrity="sha384-9gVQ4dYFwwWSjIDZnLEWnxCjeSWFphJiwGPXr1jddIhOegiu1FwO5qRGvFXOdJZ4" crossorigin="anonymous">

</head>
<body>
<div class="container col-sm-4 col-md-7 col-lg-4 mt-5">
    <div class="card">
        <h3 class="card-header" id="monthAndYear"></h3>
        <table class="table table-bordered table-responsive-sm" id="calendar">
            <thead>
            <tr>
                <th>Sun</th>
                <th>Mon</th>
                <th>Tue</th>
                <th>Wed</th>
                <th>Thu</th>
                <th>Fri</th>
                <th>Sat</th>
            </tr>
            </thead>

            <tbody id="calendar-body">

            </tbody>
        </table>


        <br/>
    </div>
</div>
<!--<button name="jump" onclick="jump()">Go</button>-->

<!-- Optional JavaScript for bootstrap -->
<!-- jQuery first, then Popper.js, then Bootstrap JS -->
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js"
        integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo"
        crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.0/umd/popper.min.js"
        integrity="sha384-cs/chFZiN24E4KMATLdqdvsezGxaGsi4hLGOzlXwp5UZB1LY//20VyM2taTB4QvJ"
        crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.0/js/bootstrap.min.js"
        integrity="sha384-uefMccjFJAIv6A+rW+L4AHf99KvxDjWSu1z9VI8SKNVmz4sk7buKt/6v9KI65qnm"
        crossorigin="anonymous"></script>


</body>
</html>

JavaScript

let today = new Date();
let currentMonth = today.getMonth();
let currentYear = today.getFullYear();
let selectYear = currentYear
let selectMonth = currentMonth

let months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];

let monthAndYear = document.getElementById("monthAndYear");
showCalendar(currentMonth, currentYear);


function next() {
    currentYear = (currentMonth === 11) ? currentYear + 1 : currentYear;
    currentMonth = (currentMonth + 1) % 12;
    showCalendar(currentMonth, currentYear);
}

function previous() {
    currentYear = (currentMonth === 0) ? currentYear - 1 : currentYear;
    currentMonth = (currentMonth === 0) ? 11 : currentMonth - 1;
    showCalendar(currentMonth, currentYear);
}

function jump() {
    currentYear = parseInt(selectYear.value);
    currentMonth = parseInt(selectMonth.value);
    showCalendar(currentMonth, currentYear);
}

function showCalendar(month, year) {

    let firstDay = (new Date(year, month)).getDay();
    let daysInMonth = 32 - new Date(year, month, 32).getDate();

    let tbl = document.getElementById("calendar-body"); // body of the calendar

    // clearing all previous cells
    tbl.innerHTML = "";

    // filing data about month and in the page via DOM.
    monthAndYear.innerHTML = months[month] + " " + year;
    selectYear.value = year;
    selectMonth.value = month;

    // creating all cells
    let date = 1;
    for (let i = 0; i < 6; i++) {
        // creates a table row
        let row = document.createElement("tr");

        //creating individual cells, filing them up with data.
        for (let j = 0; j < 7; j++) {
            if (i === 0 && j < firstDay) {
                let cell = document.createElement("td");
                let cellText = document.createTextNode("");
                cell.appendChild(cellText);
                row.appendChild(cell);
            }
            else if (date > daysInMonth) {
                break;
            }

           ...