how to handle errors with api constructor

apiabilities.js

// you dont need new but can have new
var api = apiConstructor();
var success = function(res){
  console.log(res);
};
//passes error object eg. -> new Error("this is an error") 
var error = function(err){
  console.log(err.message);
};

api.addCommand('user/check_urlname').
  addCall({
    'url_name' : url_name
  }).
  sendData();
// error is the second parameter
api.complete(success, error);

// mainly handles could not recieve json

// also now you can stop api calls if user navigates away from data being loaded
// this is just a eg.
nav.onChange = function(){
  // this is the actual call
  api.cancel();
  // then you can start another call
  api.addCommand('user/check_urlname').
    addCall({
      'url_name' : url_name
    }).sendData();
  api.complete(success, error);
}