JavaScript callback an array with values pushed through a loop

Question

I have a Node.Js web app with Express.Js that reads values from xml files, store values from all xml files into an array with sub-array represent the separation of per xml file. At the moment, I have the following code on the Node:

app.get('/get_software_requests', function (req, res) {
console.log("loading software requests");
requests_callback(function(all_software_requests){
    console.log(all_software_requests);
});

function requests_callback(callback){
    loadAllSoftwareRequests(function(all_software_requests){
    callback(all_software_requests);
    });
 }
});

function loadAllSoftwareRequests(callback){
console.log("loading requests");
fs.readdir("/project_requests", function(error, files) {
    files.forEach(filename => {
        var software_request = new Array();
        loadSoftwareRequestXML(filename, software_request, function(software_request){
            all_software_requests.push(software_request);
            callback(all_software_requests);
        });
    });
 });
}

function loadSoftwareRequestXML(filename, software_request, callback){
var xmlparser = new xml2js.Parser();
var filepath = "/project_requests/" + filename;
fs.readFile(filepath, "utf-8", function(error, values){
    xmlparser.parseString(values, function(error, xmlfile){
        var xmldata = xmlfile;
        date_requested = xmldata.ProjectRequest.DateRequested;
        client_org = xmldata.ProjectRequest.ClientOrganization;
        proposed_budget = xmldata.ProjectRequest.ProposedBudget;
        contact_name = xmldata.ProjectRequest.ContactName;
        delivery_date = xmldata.ProjectRequest.DeliveryDate;
        requirements = xmldata.ProjectRequest.UserRequirements;
        software_request.push(date_requested);
        software_request.push(client_org);
        callback(software_request);
    });
 });
}

So far, for "console.log(all_software_requests);" on the main app.get, the console outputs:

I want the Node to only return the last iteration result, like

Any help or suggestion is appreciated. Please feel free to comment. Thanks.

Answer 1

You can use native promises for that:

Promise.all(files.map(
    filename => new Promise(ok => load(filename, request => ok(request)))
)).then(requests => callback(requests));

I mess with promise/callback style here to minify your code editions.
Better to use promises instead of callbacks in client code too.

Then it becomes just:

let loadAll = files => Promise.all(files.map(load));
let load = filename => {/*return some promise with result*/}

Without promises at all it is not too difficult:

let c = files.length; // initialize a counter
files.forEach(filename => {
    var software_request = new Array();
    loadSoftwareRequestXML(filename, software_request, function(software_request){
        all_software_requests.push(software_request);
        if(!--c) { // all async calls are finished
          callback(all_software_requests);
        }
    });
});

Answer 2

You could also add my "next" method that will handle the looping for you. This has worked well for me in these types of situations.

  app.get('/get_software_requests', function (req, res) {
    console.log("loading software requests");
    requests_callback(function(all_software_requests){
        console.log(all_software_requests);
    });

function requests_callback(callback){
    loadAllSoftwareRequests(function(all_software_requests){
    callback(all_software_requests);
    });
  }
});

function loadAllSoftwareRequests(callback){
console.log("loading requests");
fs.readdir("/project_requests", function(error, files) {
    files.forEach(filename => {
        var software_request = new Array();
        loadSoftwareRequestXML(filename, software_request, function(software_request){
            all_software_requests.push(software_request);
            callback(all_software_requests);
        });
    });
 });
}

function loadSoftwareRequestXML(filename, software_request, callback){
var xmlparser = new xml2js.Parser();
var filepath = "/project_requests/" + filename;
fs.readFile(filepath, "utf-8", function(error, values){
  var index = 0;
  var next = function () {
    if (index >= values.length) {
      callback(null, values);
      return;
    }
    var value = values[index];
    xmlparser.parseString(value, function(error, xmlfile){
      var xmldata = xmlfile;
      date_requested = xmldata.ProjectRequest.DateRequested;
      client_org = xmldata.ProjectRequest.ClientOrganization;
      proposed_budget = xmldata.ProjectRequest.ProposedBudget;
      contact_name = xmldata.ProjectRequest.ContactName;
      delivery_date = xmldata.ProjectRequest.DeliveryDate;
      requirements = xmldata.ProjectRequest.UserRequirements;
      software_request.push(date_requested);
      software_request.push(client_org);
      value.software_request = software_request;
      index++;
      next()
    });
  }
  next();
 });
}