JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title>Cwiczenia</title>
    <script src="//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
    <script type="text/javascript" src="main.js"></script>
    <link rel="stylesheet" type="text/css" href="main.css">
    <link rel="stylesheet" type="text/css" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css">
</head>
<body>
<div id="all">
<div>
<h1>Jest godzina: </h1> <h1><span id="godz"></span> : <span id="min"></span> : <span id="sec"></span> : <span id="milisec"></span></h1>
</div>
<button id="1">1</button><button id="2">2</button>
</div>
<div>
    <p>Zatrzymałeś zegar o:</p>

</div>


</body>
</html>

JavaScript

var ms;
function whatistime(){
    var timenow =new Date();
    var h = timenow.getHours();
    var m = timenow.getMinutes();
    var s = timenow.getSeconds();
    var ms1 = Math.round(timenow.getMilliseconds() / 100);
    var ms2 = checkTime(Math.round(timenow.getMilliseconds() / 10));
    $("#0").click(function(){
        $("#milisec").fadeOut();
    });
    $("#1").click(function(){
        setInterval(function(){ms = ms1}, 100);
        $("#milisec").fadeIn();
    });
    $("#2").click(function(){
        setInterval(function(){ms = ms2}, 10);
        $("#milisec").fadeIn();
    });

    $("#godz").text(checkTime(h));
    $("#min").text(checkTime(m));
    $("#sec").text(checkTime(s));
    $("#milisec").text(ms);
    setTimeout(whatistime, 10);


}
function checkTime(i) {
    if (i<10) {
        i = "0" + i;
    }
    return i;
}

whatistime();