This is a simple way to preload a few images using only CSS.

#imagePreload {
       display: inline;
       height: 0px;
       width: 0px;
       background-image: url(imagePath1.extension);
       background-image: url(imagePath2.extension);
       background-image: url(imagePath3.extension);
       background-image: url(imagePath4.extension);
       background-image: url();
}

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1. Set Style Dynamically With JavaScript