How to wait for multiple API calls to reutrn?

I have an array of APIs to query. For example var urls = ['example.org?x=1', 'example.org?x=2,3'] How can I have ReactJS wait for all the responses to come back before responding to the client?

I’ve tried a modification @Shanoor’s answer from Promises with http.get node.js but the result to the client is empty ("").

var http = require('http');
var urls = ['example.org', 'example2.org', '...'];

var done = 0;
var result = [];

function callback(index, data) {
  result[index] = data;
  done++;
  if (done == urls.length) {
    result.forEach(console.log);
    //I tried using the resp object here to return result[] but the data seemed corrupt 
  }
}

function processUrl(url, index) {
  var finalData = '';
  http.get(url, function(response) {
    response.setEncoding('utf8');
    response.on('data', function(data) {
      finalData += data;
    });
    response.on('error', console.error);
    response.on('end', function() {
      callback(index, finalData);
    })
  });
}

app.get("/api/blah", (resp) => {
  urls.forEach(processUrl);
  //resp(result); this would result in an empty response
}