var Gallery = {
	attach: function() {
		var gallery = document.getElementById("gallery");

		if (!gallery) return;

		var thumbs = gallery.getElementsByTagName("a");

		for (var link, i = 0; link = thumbs[i]; i++)
			link.onclick = Gallery.change;
	},

	change: function() {
		var main = document.getElementById("main-screen");

		if (!main) return;

		main.src = this.href;

		return false;
	},

	load: function() {
		var prevLoad = window.onload;
		window.onload = prevLoad ?
			function() {
				Gallery.attach();
			}
			: Gallery.attach;
	}
}

Gallery.load();