NodeJS - Send multiple requests and process all responses in one callback

Question

I'm trying to find a way to send multiple requests (using Express) and process all the response in one function.

Here's my code :

  // In router.js
  app.get('/api/FIRST_PATH', CALLBACK_FUNCTION_A );

 // In CALLBACK_FUNCTION_A file :
 module.exports = function (req, response) {
   CALLBACK_FUNCTION_TO_SERVICE_A();
   CALLBACK_FUNCTION_TO_SERVICE_B();
   CALLBACK_FUNCTION_TO_SERVICE_C();
}

My problem is to send the requests CALLBACK_FUNCTION_TO_SERVICE_A, CALLBACK_FUNCTION_TO_SERVICE_B and CALLBACK_FUNCTION_TO_SERVICE_C and then retrieve all the results in another function to process them.

Any help would be greatly appreciated.

use request-promise to do requests that return a promise, then do something when those promises are finished — Fabio Antunes
– Fabio Antunes, Commented Jun 2, 2016 at 10:17

coyotte508 · Accepted Answer · 2016-06-02 12:55:56Z

3

You can learn more about the new js standard and use Promise.

// In CALLBACK_FUNCTION_A file :
module.exports = function (req, response) {
   var promises = [CALLBACK_FUNCTION_TO_SERVICE_A(), 
      CALLBACK_FUNCTION_TO_SERVICE_B(),
      CALLBACK_FUNCTION_TO_SERVICE_C()];

   Promise.all(promises).then( function(results) {
       //results is an array
       //results[0] contains the result of A, and so on
   });
}

Of course CALLBACK_FUNCTION_TO_SERVICE_A() and such need to return Promise objects. You form a function like this:

function asyncFunction(callback) {
   //...
   callback(result);
}

You can create a Promise like this:

var p = new Promise(asyncFunction);

It'll start running the function, and supports the Promise interface.

So for example, either use request-promise or you can do something like:

function CALLBACK_FUNCTION_TO_SERVICE_A() {
   var worker = function(callback) {
       app.get('/api/FIRST_PATH', callback);
   };

   return new Promise(worker);
}

You can read more about Promise and how to also easily handle errors.

edited Jun 2, 2016 at 12:55

answered Jun 2, 2016 at 12:10

coyotte508

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1 Comment

Ismail H Over a year ago

Mind Blowing ! Thanks a lot

Aman Gupta · Accepted Answer · 2016-06-02 11:21:10Z

1

You could use async parallel. You can keep all your API calls as async.parallel array or JSON(Example uses Array).

async.parallel(
 [
    function(done){
      reqServcieA(..., funnction(err, response){
        if(err) done(err,null);
        done(null, response);
      }
    },
    function(done){
      reqServcieA(..., funnction(err, response){
        if(err) done(err,null);
        done(null, response);
      }
    },
    ...// You can keep as many request inside the array

 ], function(err,results){
   // Will be called when all requests are returned
   //results is an array which will contain all responses as in request arry
    //results[0] will have response from requestA and so on
 });

answered Jun 2, 2016 at 11:21

Aman Gupta

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1 Comment

Ismail H Over a year ago

I had tried using async parrallel. I guess I didn't use it right. Thank you for the answer.

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