Convert XML files to JSON and move them

Question

What the code does (tested basic, no errors, usecase):

• Reads all XML files (ending in .yin) from a directory.
• converts each to JSON
• store it in another directory, with the same basename as source file
• ... with .yin replaced by .json

Overt issues:

• The code has too many nested functions
• walk module's next() method in multiple places
• lack of robust error checks and ensuring no uncaught errors left behind

Q. How to refactor the code using Node.js best practices? (things like):

• flatten out the nesting.
• avoiding having to remember to call next(), on all if(err) scenarios.
• does any other (than those included) module improve readability/efficiency?

Two Node.js files, a module and a main file invoking that module, are attached.

File 1: Main:

// main.js
var path = require ('path');
var yin2json = require ('./yin2json');
console.log ("__dirname: " + __dirname);
var templateDir = path.resolve (__dirname, "resources", "mgmtDataTemplates");
var yinDir = path.resolve (templateDir, "yins");
var jsonDir = path.resolve (templateDir, "jsons");
yin2json.convertYins (yinDir, jsonDir);

File 2: Module:

// yin2json.js
 var fs = require('fs');
 var path = require('path');
 var walk = require('walk');
 var xml2js = require('xml2js');
 var jsonDir ;
 var convertYins = function (yin_dir, json_dir) {
 jsonDir = json_dir;
 var walker = walk.walk(yin_dir, { followLinks: true });
 walker.on("errors", fDirWalkError);
 walker.on("end", fDirWalkEnd);
 walker.on("file", fDirWalkFile);
 }
 function fDirWalkError (err) {
 console.log ("fDirWalkError: " + err);
 next (err);
 }
 function fDirWalkEnd () {
 console.log ("======= End of directory walk");
 }
 function fDirWalkFile (root, fileStat, next) {
 if (fileStat.name.indexOf(".yin") < 0) {
 console.log ("skipping file " + fileStat.name + " (does not end in .yin)");
 return;
 } else {
 var yin_file = path.resolve(root, fileStat.name);
 console.log ("yin file: " + yin_file);
 fs.readFile(yin_file, function (err, data) {
 if (err) {
 console.log ("error reading file:" + yin_file);
 next (err);
 }
 xml2js.parseString (data, function (err, json_obj) {
 if (err) {
 console.log (err);
 next (err);
 }
 var json_string = JSON.stringify(json_obj, null, 2);
 var json_file = path.resolve (jsonDir, path.basename(yin_file).replace(/\.yin$/, ".json"));
 console.log ("json file: ", json_file);
 fs.writeFile(json_file, json_string, "utf8", function (err) {
 if (err) {
 console.log ("error converting yin (%s) to json(%s)", yin_file, json_file);
 next (new Error ("error converting yin(" + yin_file + ") to json(" + json_file + ")"));
 }
 else {
 console.log ("Converted yin (%s) to json(%s)", yin_file, json_file);
 }
 });
 });
 });
 }
 next ();
 }
module.exports.convertYins = convertYins;

• SuperBiasedMan: Welcome to Code Review! As we all want to make our code more efficient or improve it in one way or another, try to write a title that summarizes what your code does, not what you want to get out of a review. For examples of good titles, check out Best of Code Review 2014 - Best Question Title Category You may also want to read How to get the best value out of Code Review - Asking Questions. I changed yours, but if you think it's misleading please improve it.

Answer 1

Try using a Promise library like bluebird. it will save you from callback hell and allow you to write your code synchronously.

let Promise = require('bluebird'),
 fs = Promise.promisifyAll(require('fs'))
function readAllFilesInDir(pathArr) {
 // assume i get all files path as array here 
 let allPromises = pathArr.forEach(function (path) {
 return fs.readFileAsync(path, 'utf8')
 })
 return allPromises
}
function doYourThing() {
 // body...
}
readAllFilesInDir(pathArr)
.then(doYourThing)