create a json object with responses from different async functions

Question

My goal is to create a JSON object, from a paragraph of text, that I can then insert as a document into MongoDB. I'm using nodejs and wanted to go for the async approach.

My JSON has parameters like so

{
   height:height,
   weight:weight
}

My logic is this

create a module with async functions that parse the text and extract weight and height using regex.

but then how would I combine all the responses from these functions into one JSON that I can import at once?

I'm thinking something like this

var get_height = require().height;
var get_weight = require().weight;

exports.contr = function(){
   var height,
       weight;
   get_height(text, function(err, res){
      if(err)
          throw(err)
      height=res;
   });

   get_weight(text, function(err, res){
      if(err)
          throw(err)
      weight=res;
   });
   //All other async functions
   combine_json(height, weight, ... , function(err, res){
       if(err)
          throw(err);

       console.log(res); //the json was successfully inserted into mongoDB
   }); 
}

I find async confusing and in the above example I'm not sure about two things

wouldn't combine_json run without waiting for the data from the previous two functions (weight, height)
what is the best practice to handle such cases? Should i just use sync functions and wait top-to-bottom for each one to do its thing and then run the final one or I can leverage async?

deceze · Accepted Answer · 2016-05-12 01:01:30Z

1

The simplest way to wait for the results of two independent asynchronous functions is to use promises and Promise.all. For this we'll assume get_height and get_weight return a Promise and can be used as such:

get_height().then(function (height) { console.log(height); });

Then it's trivial to combine two of those promises:

Promise.all([get_height(), get_weight()]).then(function (results) {
    combine_json(results[0], results[1]);
});

See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise for documentation and details.

answered May 12, 2016 at 1:01

deceze♦

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1 Comment

Ando Over a year ago

just a 'callback' that these promises are totally what i needed but they are hard to wrap my head around them. Thanks for the response, man.

Jose Hermosilla Rodrigo · Accepted Answer · 2016-05-12 01:13:33Z

0

If you do not know nothing of Promises, you first should know how callbacks works. If you do not want a elegant solution with Promise.all() and you just want your code working, you need nested functions. When you are inside get_height callback you should to call get_weight and same when you are inside get_weight callback you should call combine_json() . The only problem is that you have to wait for get_height to call get_weight. This is solved with Promise.all() as it's said.

   get_height(text, function(err, height){
      if(err)
          throw(err);
      get_weight(text, function(err, weight){
         if(err)
            throw(err);
         //All other async functions
         combine_json(height, weight, ... , function(err, res){
             if(err)
                throw(err);
             console.log(res); //the json was successfully inserted into mongoDB
         }); 
      });
   });

edited May 12, 2016 at 1:13

answered May 12, 2016 at 1:07

Jose Hermosilla Rodrigo

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1 Comment

Jose Hermosilla Rodrigo Over a year ago

I said in my answer that thisis the problem.

user663031 · Accepted Answer · 2016-05-12 02:34:54Z

0

Promises are your best bet, but if you don't want to use them for some reason and prefer the callback style, then

function get_height_and_weight(text, callback) {
  var have_height = false;
  var have_weight = false;
  var result = {};

  get_height(text, function(err, height) {
    if (err) callback(err);
    have_height = true;
    result.height = height;
    if (have_weight) callback(null, result);
  });

  get_weight(text, function(err, weight) {
    if (err) callback(err);
    have_weight = true;
    result.weight = weight;
    if (have_height) callback(null, result);
  });
}

This is a special case of the parallel async call case which could be handled better by async.parallel.

answered May 12, 2016 at 2:34

user663031

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