seasons.js

(function () {
	function getCurrentSeason() {
		var now = new Date();
		var currentYear = now.getFullYear();

		if (now < new Date(currentYear, 2, 1)) {
			// [Jan 1 ~ Mar 1)
			return 'winter';
		}
		if (now < new Date(currentYear, 5, 1)) {
			// [Mar 1 ~ Jun 1)
			return 'spring';
		}
		if (now < new Date(currentYear, 8, 1)) {
			// [Jun 1 ~ Sep 1)
			return 'summer';
		}
		if (now < new Date(currentYear, 11, 1)) {
			// [Sep 1 ~ Dec 1)
			return 'autumn';
		}
		// [Dec 1 ~ Dec 31]
		return 'winter';
	}

	var header = document.getElementById('header');
	switch (getCurrentSeason()) {
		case 'winter':
			header.style.backgroundImage = "url('/Logo_season1.jpg')";
			break;
		case 'spring':
			header.style.backgroundImage = "url('/Logo_season2.jpg')";
			break;
		case 'summer':
			header.style.backgroundImage = "url('/Logo_season3.jpg')";
			break;
		case 'autumn':
			header.style.backgroundImage = "url('/Logo_season4.jpg')";
			break;
	}
})();

how do I test if I want to know if each season is running? like how to change the months? thanks!