Timer Javascript

timer.js

window.onload = function () {
				
				var timeout;
				var MIN; 
				var SEC;
				document.getElementById("startTimer").onclick=function(){startTimer()}

				function startTimer(){
					MIN = document.getElementById("min").value;
					SEC = document.getElementById("sec").value;
					
					document.getElementById("startTimer").value = "Stop";
					document.getElementById("startTimer").id = "stopTimer";
					
					document.getElementById("stopTimer").onclick=function(){stopTimer()}
					
					refreshTimer(MIN, SEC);
				}
			
				function stopTimer(){
					document.getElementById("stopTimer").value = "Start";
					document.getElementById("stopTimer").id = "startTimer";
					
					document.getElementById("startTimer").onclick=function(){startTimer()}
					timeout = clearTimeout(timeout);
				}
						
				function refreshTimer(MIN, SEC){
					if(SEC == 0){
						MIN = MIN - 1;
						SEC = 59;
					}else{
						SEC = SEC - 1;
					}
					
					if(MIN+SEC > 0){
						document.getElementById("min").value = MIN;
						document.getElementById("sec").value = SEC;
						timeout = setTimeout(refreshTimer, 1000, MIN, SEC);
					}else{
						document.getElementById("min").value = MIN;
						document.getElementById("sec").value = SEC;
					
						document.getElementById("stop").id = "start";
					}
				}
			}