You can preload images like this:
function preloadImages(srcs) {
if (!preloadImages.cache) {
preloadImages.cache = [];
}
var img;
for (var i = 0; i < srcs.length; i++) {
img = new Image();
img.src = srcs[i];
preloadImages.cache.push(img);
}
}
// then to call it, you would use this
var imageSrcs = ["src1", "src2", "src3", "src4"];
preloadImages(imageSrcs);
Just fill in the URLs in the imageSrcs
array and run this when your page first runs. The sooner you run it, the earlier your images will be available.
FYI, a related answer here: Image preloader javascript that supports events.