试试是否可行。
(function(){
var doc = getCurrentDocument();
var gpswbk = doc.getItemValueAsString("gps"); //获取的值是{"latitude":11,"longitude":11,"address":"xxxx"}
gpswbk="["+gpswbk+"]";
var jsonArray = new Packages.org.json.JSONArray(gpswbk);
for(var i=0;i<jsonArray.length();i++){
var jsonObject = jsonArray.getJSONObject(i);
var address= jsonObject.getString("address");
}