Michael Hartmayer

var TimerCountdown = function() {
  var oOnZero     = function(){},
      oOnUpdate   = function(){},
      oTimer,
      iCurTime    = 0;
 
  function CreateTimer() {
    oTimer = setInterval(IterateTimer, 1000)
  }
 
  function DestroyTimer() {
    clearInterval( oTimer );
  }
 
  function IterateTimer() {
    iCurTime = iCurTime - 1;
    oOnUpdate({
      Seconds: iCurTime,
      Minutes: parseInt( iCurTime / 60 ),
      Hours: parseInt( iCurTime / 60 / 60 )
    });
 
    if( iCurTime <= 0 ) {
      DestroyTimer();
      oOnZero();
    }
  }
 
  return {
    SetTime: function( iSeconds ) {
      iCurTime = iSeconds;
    },
    Start: function() {
      CreateTimer();
    },
    Stop: function() {
      DestroyTimer();
    },
    Time: function() {
      return iCurTime;
    },
    Add: function( iSeconds ) {
      iCurTime = iCurTime + iSeconds;
    },
    Subtract: function( iSeconds ) {
      iCurTime = iCurTime - iSeconds;
    },
    OnUpdate: function( cbFunction ) {
      oOnUpdate = cbFunction;
    },
    OnZero: function( cbFunction ) {
      oOnZero = cbFunction;
    }
  };
};