Untitled

<div class="home-intro show-for-medium-up" id="home-intro">
</div>

.home-intro{
  background-image: url("../images/1.png");
  background-color:grey;
  height:500px;
  color:$white;
  text-align:center;
  }

<script>


function randomImage(){
  var images = [
   '../images/1.png',
   '../images/2.png',
   '../images/3.png'];
  var size = images.length;
  var x = Math.floor(size * Math.random());
  console.log(x);
  var element = document.getElementsByClassName('home-intro');
  console.log(element);
  element[0].style["background-image"] = "url("+ images[x] + ") no-repeat;";
}

document.addEventListener("DOMContentLoaded", randomImage);

<body onload="randomImage()">`

var x=Math.floor(size * Math.random());

document.getElementById("home-intro").style.backgroundImage = "../images/" + x + ".png";