[vandy]

Как вариант:

div=document.createElement("DIV")
div.style.cssText="width:100px;height:100px;border :1px solid blue;"
document.body.appendChild(div);
user_obj=new UserObject();
user_obj.bg.call(div);

function UserObject(){
  var me = this;
  me.color="blue";
  me.bg=function(){
   this.style.backgroundColor=me.color; 
  }
}