// Seconds left in the user's session
var timeLimit = 300;

// The element to contain the timer count
var timeLimitSpan;

// The countdown timer
var timer;

function sessionTimerInit()
{
	timeLimitSpan = document.getElementById('timelimit');
	timer = setInterval(updateTimer, 1000);
}

function updateTimer()
{
	if (--timeLimit < 0)
	{
		clearInterval(timer);
		return;
	}
	
	var minutes = parseInt(timeLimit / 60);
	var seconds = (timeLimit % 60);
	
	timeLimitSpan.innerHTML =  minutes + ':' + (seconds < 10 ? '0' : '') + seconds;
}

addEvent(window, 'load', sessionTimerInit);