Wait for request to finish Node.js

Question

I am currently having an issue with figuring out how to wait for the request to finish before returning any data. I do not believe I can do this with a Callback and I have n

Answer 1

You need to use callbacks. Change your API grabber to this:

function getItems(amount, callback) {
// some code... 
request({
  url: url,
  json: true
}, function (error, response, body) {
   // some code...
   if (!error && response.statusCode === 200) {
      // some code    
      callback(items); <-- pass items to the callback to "return" it
   }
})
}

Then change the xml generator to also accept callbacks:

function generateXML(callback){
// Code to generate XML
var API = require('./API');
API.getItems("5",function(response){
  for(var i = 1; i <= response.length; i++)
  {
    // more code to generate further XML using the API response
  }

  // Finish generating and return the XML
  callback(xml_result); // <-- again, "return" the result via callback
});
}

Then in your server code do:

var xml = require('./XMLGenerator');
response.writeHead(200, {'Content-Type': 'text/xml'});
xml.generateXML(function(xmlstring){
    response.write(xmlstring);
    response.end();
});

Answer 2

Do these changes since request is async, use callbacks.

API.getItems("5", function(rs){
      var response = rs;
      for(var i = 1; i <= response.length; i++)
      {
      // more code to generate further XML using the API response
      }

      // Finish generating and return the XML
    }

});


...
function getItems(sort_by, amount, callback) {...

...
callback(items); //Instead of return items;

...

You cannot return from an async call, which is request module in your case. In such cases you can either use promises or callbacks. This is a solution with callback.

The actual problem of it returning undefined is it doesnot wait for var response = API.getItems("5"); to execute completely and executes the next line and hence you get response as undefined. I hope you get the point.\

Also I hope

response.writeHead(200, {'Content-Type': 'text/xml'});
response.write(xml.generateXML());
response.end();

is somewhere inside some callback of an API or http.createServer.