Returning a object from call back function, so that a wrapping function can return the same object in node.js/express

Question

Returning a object from call back function, so that a wrapping function can return the same object in node.js/express

I am trying to return an object that I am constructing from data obtained from a call to a third party API. I am using the Request(https://github.com/mikeal/request) module to accomplish the same.

However, I want to return this object from the callback function.

My request call is a part of a javascript function and I want this outer function to be able to return the newly constructed object. I am facing problem due to non-blocking nature of node.js as whenever I try to return object from the outer function, it returns an empty object because the callback function has not yet contructed the object.

How can I achieve this?

function getData(url){

  var myWeatherData = new Object();
  var data;

  request(url, function (error, response, body) {

    if (!error && response.statusCode == 200) {

      data = JSON.parse(body);

      myWeatherData.locationName = data.current_observation.display_location.full;
      myWeatherData.weather = data.current_observation.weather; 
      myWeatherData.temperature_string = data.current_observation.temperature_string;
      myWeatherData.relative_humidity = data.current_observation.relative_humidity;
      myWeatherData.wind_string = data.current_observation.wind_string;
      myWeatherData.feelslike_string = data.current_observation.feelslike_string;

    }
    return myWeatherData; // THIS IS A RETURN FROM CALL BACK 
  });   
// return myWeatherDataArr; -- THIS RETURNS AN EMPTY 
};

javascript
node.js
express
node-request

Answer 1

getData finishes well before the callback is called by the asynchronous request function - you cannot return from getData something that is not there yet.

If you need some code to work with myWeatherData, pass that code as another callback to getData:

function getData(url, callback){

  request(url, function (error, response, body) {

    if (!error && response.statusCode == 200) {
      var data = JSON.parse(body);
      var myWeatherData = new Object();    
      myWeatherData.locationName = data.current_observation.display_location.full;
      ...
      myWeatherData.feelslike_string = data.current_observation.feelslike_string;

      callback(myWeatherData);
    }
  }); 
}

In response to your comment I can only repeat the first sentence of my answer. And:

app.get('/', function(req, res){ 
  var url = urlPrefix + myCities.state + '/' + myCities.city + '.json'; 
  getData(url, function(aWeatherData) {
    res.render('index', aWeatherData); 
  });
});