Simple timer with callback.

timer.js

function Timer(timerLength, countdownCallback) {
	
	var intervalId = null,
		currentInterval;
	
	this.start = function() {
		
		if (timerLength <= 0) return false;
		
		currentInterval = timerLength;
		intervalId = setInterval(function() {
			
			currentInterval--;
			countdownCallback(currentInterval);
			
			if (currentInterval <= 0) {
				clearInterval(intervalId);
			}
		}, 1000);		
	};
	
	this.stop = function() {
		clearInterval(intervalId);
	};
	
	this.restart = function() {
		clearInterval(intervalId);
		this.start();
	};
}

module.exports = Timer;