//  one: passes up the error from two()
function one(cb){
	two(function(err, data){
		if(err) return cb('one ' + err);
		return cb(null, data);
	});
}

//  two: passes up the error from three()
function two(cb){
	three(function(err, data){
		if(err) return cb('two ' + err);
		return cb(null, data);
	});
}

//  three: always returns an error
function three(cb){
	cb('three: something bad happened');
}

//  kick off one(), log the inevitable error with a simple function trace
one(function(err, data){
	if(err) {
		console.log(err);
		return;
	}
});

//  output:
//  one two three: something bad happened