gistfile1.js

function preloadImages(imageUrls, callback) {
	var images = [],
		imagesLen = imageUrls.length,
		loaded = 0,
		image;
		
	function imageLoaded() {
		if (++loaded == imagesLen) {
			callback(images);
		}
	}
	
	for (var i = 0; i < imagesLen; i++) {
		image = new Image();
		image.onload = imageLoaded;
		image.src = imageUrls[i];
		images.push(image);
	}
}