xmlhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
        var valr5 = this.responseText;
        document.getElementById("countdown").innerHTML = valr5;
        
        if (valr5 == '00:00'){
            window.location = "index.php";
        }   
    }
};

On Ajax call, in return responseText, I am getting remaining minutes and seconds in this format '1.30'. (it can be anything like '00.28' in place of '1.30')

I wanted decrement it by 1 till '00:00' but with accuracy of 1 sec and show that countdown in "countdown" div

Please can anyone guide me on this.