startTimer.js

function startTimer(){
    let shc = new Date();
    var h=shc.getHours();
    var m=shc.getMinutes();
    var s=shc.getSeconds();

    var datestr = shc.toDateString();

// Adding zero in fron of a number
    h=addZero(h);
    m=addZero(m);
    s=addZero(s);

    document.getElementById('tmr').innerHTML = datestr + ' ' + h + ':' + m  + ':' + s;
    t=setTimeout('startTimer()', 500);
}

function addZero(z){
    if(z<10){
        z = "0" + z;
    }
    return z;
}