JSFiddle - React, Tailwind, and code Playground

HTML

<span id="timer"></span>

JavaScript

function countdown(timestamp) {

		var hours = parseInt( Math.abs( (timestamp/3600) ) );
		var minutes = parseInt( Math.abs( ((timestamp%3600)/60) ) );
		var seconds = parseInt( Math.abs( ((timestamp-hours*3600-minutes*60) ) ) );

		if(hours<10)
			hours='0'+hours.toString();
		if(minutes<10)
			minutes='0'+minutes.toString();
		if(seconds<10)
			seconds='0'+seconds.toString();

		var text = hours + ':' + minutes + ':' + seconds;
		document.getElementById('timer').textContent = text;
		
		
	}

	var sec = 410;
	
	var timer = setInterval(function(){ 
		countdown(sec);
		sec -=1;
		
		if (sec <= 0) clearInterval(timer);
		
	}, 1000);