code: public int unshift(Object obj) {
          if (obj instanceof JavascriptObject) {
              //jsObject.setSlot(length(), ((JavascriptObject) obj).getJSObject());
              content.put(((JavascriptObject) obj).getJSObject(), (JavascriptObject) obj);
          }
          return checkInteger(invokeJavascript("unshift", obj), 0);
      }
docs: unshift() 	Adds new elements to the beginning of an array, and returns the new length