Tryit Editor v1.8

Source Code:
<!DOCTYPE html> <html> <body> <p>A script on this page starts this clock:</p> <p id="demo"></p> <button onclick="myStopFunction()">Stop time</button> <script> var myVar=setInterval(function(){myTimer()},1000); function myTimer() { var d=new Date(); var t=d.toLocaleTimeString(); document.getElementById("demo").innerHTML=t; } function myStopFunction() { clearInterval(myVar); } </script> </body> </html>
Result:
W3Schools.com - Try it yourself