gistfile1.js

function newElement(object_name, method, resource, controller, div, prompt_text){
  var name = prompt(prompt_text);
  if(name) {
    field = object_name + "[name]";
    $.post("/" + controller, {'element[name]' : name}, function(response) {
      var html = "<select name='" + object_name + "[" + method + "]' id='" + object_name + "_" + method + "'><option value=''/>";
      for(var i=0;i<response.length;i++){
        html += "<option value='" + response[i][resource].id + "'>" + response[i][resource].name + "</option>"
        
        if(response[i][resource].name == name) {
          var id = response[i][resource].id
        }
      }
      $("#" + div).html(html);
      $("#" + object_name + "_" + method).children("[value=" + id + "]").attr("selected", "selected")
    }, "json");
  } else {
    window.alert("Debe introducir un nombre"); 
  }
}