var chairsURL = "imgs/chairs1.jpg";

if (document.images) {
     var chairs1 = new Image();
     chairs1.src = "imgs/chairs1.jpg";

     var chairs2 = new Image();
     chairs2.src = "imgs/chairs2.jpg";
	 
	 var chairs3 = new Image();
	 chairs3.src = "imgs/chairs3.jpg";
}

function changeChairs() {
     if (document.images) {
        if (chairsURL == "imgs/chairs1.jpg") chairsURL = "imgs/chairs2.jpg";
		else if (chairsURL == "imgs/chairs2.jpg") chairsURL = "imgs/chairs3.jpg";
		
         document.myChairs.src = chairsURL;
	}
}