// JavaScript Document 
var aryImages = new Array(2); 
aryImages[0] = "images/image1.jpg"; 
aryImages[1] = "images/image2.jpg"; 
aryImages[2] = "images/image3.jpg"; 
aryImages[3] = "images/image4.jpg"; 

for (i=0; i < aryImages.length; i++) { 
var preload = new Image(); 
preload.src = aryImages[i]; 
} 
function swap(imgIndex) { 
document['imgMain'].src = aryImages[imgIndex]; 
}