Answers for "image style javascript"

js style background image by id

document.getElementById('Demo').style.backgroundImage = "url('Test.png')";

insert image by css

div.mydiv:after {
  content: url(image.jpg); /*url of your image*/
}

or

div.mydiv {
   width:100px; /*width of your image*/
   height:100px; /*height of your image*/
   background-image:url('image.file');
}