https://stackoverflow.com/questions/9790347/set-an-image-object-as-a-div-background-image-using-javascript
var imgSrcs = [...]; // array of URLs
var myImages = [], img;
for (var i = 0; i < 4; i++) {
img = new Image();
img.onload = function() {
// decide which object on the page to load this image into
// this part of the code is missing because you haven't explained how you
// want it to work
var div0 = document.getElementById('theDivId');
div0.style.backgroundImage = "url(" + this.src + ")";
};
img.src = imgSrcs[i];
myImages[i] = img;
}