Script.js

var hr= 0;
var min=0;
var sec=0;
var count=0;

var timer= false;

function start(){
   timer = true;
   stopwatch();
}
function stop(){
   timer= false;
   stopwatch();
}
function reset(){
    timer= false;

    hr=0;
    min=0;
    sec=0;
    count=0;

    document.getElementById("hr").innerHTML="00";
    document.getElementById("min").innerHTML="00";
    document.getElementById("sec").innerHTML="00";
    document.getElementById("count").innerHTML="00";
}

function stopwatch(){
    if(timer == true){
           count=count+1;

           if (count == 100){
               sec= sec+1;
               count=0;
           }

           if (sec == 60){
            min= min+1;
            sec=0;
           }

           if (min == 60){
                hr= hr+1;
                min=0;
               sec=0;
            }

            var hrString =hr;
            var minString = min;
            var secString =sec;
            var countString = count;

            if(hr<10){
                 hrString = "0" + hrString;
            }

            if(min<10){
                minString = "0" + minString;
           }

           if(sec<10){
            secString = "0" + secString;
       }

       if(count<10){
        countString = "0" + countString;
   }

           document.getElementById("hr").innerHTML = hrString;
           document.getElementById("min").innerHTML = minString;
           document.getElementById("sec").innerHTML = secString;
           document.getElementById("count").innerHTML = countString;

        setTimeout("stopwatch()",10);
    }
}