$(document).ready(function(){
	jQuery.preloadImages = function(){
		for(var i = 0; i<arguments.length; i++)	{
			jQuery("<img>").attr("src", arguments[i]);
		}
	};
	
	// Usage
	$.preloadImages("image/type01.jpg","image/type02.jpg","image/type03.jpg","image/type04.jpg");

	var arr = new Array("type01","type02","type03","type04"); 
	var num = Math.floor( Math.random() * arr.length );
	var cname = arr[num];
	$("body").addClass(cname);

});