if (typeof arguments[0] == 'string') {
	// preserves behaiviour in case of printf-like strings: "blabla count: %d - yeah!"
	// by just adding the timestamp to this string
	arguments[0] = prefix + " " + arguments[0];
	console.log.apply(console, arguments);
} else {
	// everything in here is exactly your unmodified code (except indentation).
	// ....
        var args = Array.prototype.slice.call(arguments);
	args.unshift(prefix);
	console.log.apply(console, args);
}