I have the below function but its not giving any errors or outputting anything, any ideas?

1. <script language="Javascript"><!--
   function getHeaderImg() {
     images = new Array(8);
    
   images[0] = "image1.jpg";
   images[1] = "image2.jpg";
   images[2] = "image3.jpg";
    
     index = Math.floor(Math.random() * images.length);
     document.write(images[index]);
   }
   
   $('.headerBKG').css({ backgroundImage: "url("+getHeaderImg()+")" });
   // --></script>