node js use promises for request from another function

Question

my node server needs to connect with other server in order to get some info and send it to the user. Since request is async in this situation I usually use addition libraries such as request-promise. But here I've got multiple calls from many points so I've created one function to handle them and this solution doesn't work.

apiCall1: function(req,res){
  var info = fetchFromOtherServer();
  console.log(info); // undefined
  res.send(info)
}
apiCall2: function(req,res){
  var info = fetchFromOtherServer();
  console.log(info); // undefined
  res.send(info)
}

function fetchFromOtherServer(){
  var options = {"method":"POST", "headers":{...},"uri":"{...}"}
  request(options, function(err,response,body){
   if(!err && response.statusCode == 200){
      console.log(body) // here is a body from other server
      return body;
    }
  }
}

So first I get an api call to function apiCall() which calls fetchFromOtherServer function. But before request is done node marks info variable as undefined and send it to the user. How can I change my code to tell node to wait until I get a response from that other server?

score 0 · Answer 1 · answered Sep 25 '17 at 01:49

You'll need a promise of your own, and you'll want to use then handlers on your promise. Take a look at promise documention and their examples.

apiCall1:

function(req,res){  var info_promise = fetchFromOtherServer();
  info_promise.then(function(info) {
    console.log(info); // undefined
    res.send(info)
  });
  # Also look into catch on promises for error
}

function fetchFromOtherServer(){
  return new promise(function(resolve, fail){
    var options = {"method":"POST", "headers":{...},"uri":"{...}"}
    request(options, function(err,response,body){
      if(!err && response.statusCode == 200){
        console.log(body) // here is a body from other server
        resolve( body);
      }
    }
  });
}

nilobarp · Answer 2 · 2017-09-25T01:59:46.340

0

If you are using ES6 go with async await. It will simplify your code a great deal.

apiCall1: function(req,res){
  let response = await fetchFromOtherServer();
  // do something with response
}
apiCall2: function(req,res){
  let response = await fetchFromOtherServer();
  // do something with response
}

async function fetchFromOtherServer(){
  let options = {"method":"POST", "headers":{...},"uri":"{...}"}
  let response = await request(options);
  return response;
}

edited Sep 25 '17 at 01:59

answered Sep 25 '17 at 01:53

nilobarp

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for now terminal sends me an error with "await" phrase. How can I include ES6 to my node project? Do something in package.json? – ampher911 Sep 25 '17 at 02:08
If you are not using `babel` or `typescript` then you need `node 7.x` for native `async` support. – nilobarp Sep 25 '17 at 02:11

node js use promises for request from another function

2 Answers2