JS简单的计时器

//显示学习计时器
var hour = 0, minute = 0, second = 0;
  var t =  0;
  var flag1;
  function studyTime()
  {
     hour=parseInt(t/60/60);
      minute=parseInt(t/60%60);
     second=parseInt(t%60);
     document.getElementById('SECOND').innerHTML=second;
     document.getElementById('HOUR').innerHTML=hour;
     document.getElementById('MINUTE').innerHTML=minute;
     t = t + 1;
     flag1 =  setTimeout("studyTime()",  1000);          
  }
  //终止学习计时器
function stopTime()
  {
     clearTimeout(flag1);
  }