var imgArray = new Array();

function preload(imgname){

		

		var img = new Image();

		img.src = imgname;

		imgArray[imgArray.length]=img;

	}
	function swapimg(obj){

	

	if(obj.src.indexOf("_on")>-1){

		obj.src=obj.src.replace("_on","_off");

	}else{

		obj.src=obj.src.replace("_off","_on");

	}

}