JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" placeholder="seconds" id="input-seconds"/>
    <span id="countdown" class="timer"></span>
    <button id="btn-timer">Set Timer</button>

JavaScript

function secondPassed() {
   // alert("Hello");
    var date = new Date();
    var seconds = date.setSeconds(date.getSeconds()+parseInt(document.getElementById("input-seconds").value,10));
   // var minutes = Math.round((seconds - 30)/60);
    //var remainingSeconds = seconds % 60;
    //if (remainingSeconds < 10) {
      //  remainingSeconds = "0" + remainingSeconds;  
    //}
   // document.getElementById('countdown').innerHTML = minutes + ":" + remainingSeconds;
    document.getElementById('countdown').innerHTML = date - seconds;
    if (seconds == 0) {
        clearInterval(countdownTimer);
        document.getElementById('countdown').innerHTML = "Buzz Buzz";
    } else {
        seconds--;
    }
}

function startTimer() {
    //setTimeout(secondPassed, 1000);
    setInterval(secondPassed, 1000);
}

document.getElementById("btn-timer").addEventListener("click", startTimer, false);
 
//var countdownTimer = setInterval('secondPassed()', 1000);