Files array return undefined in readdir - node.js

Question

I am trying to read all the files inside a nested folder. I am able to reach the innermost layer of directory but when I tried readdir method on the folders (that contains the files I want to use) the readdir method returned undefined in files array
My directory structure is like this.
main directory=logs which contains many directories like logs_of_29,logs_of_19 each of these contains different folders with names like 157486185 and each of those contains logs files
so the path to the file I am trying to read content of will be
logs\logs_of_41\1565605874284\file.json
How do I read data of this nested file
I have tried following
var http = require('http');
var fs = require('fs');
http.createServer(function (requests, response) {
handle_files()
}).listen(8080)
handle_files = () => {
// get the list of directories of logs_of_109
fs.readdir('logs_of_109', function (error, files) {
files.map(file => {
var sub_directory = file
// get list of all the directories inside logs_of_109 subfolders
fs.readdir('logs_of_109/' + sub_directory, function (error, files) {
var sub_directory2 = files
console.log('logs_of_109/' + sub_directory + sub_directory2)
files.map(file => {
fs.readdir('logs_of_109/' + sub_directory + sub_directory2, function (error, files) {
files.map(file => { console.log(file) })
})
})
})
})
})
}
Now the file in the innermost loop gives me undefined. Also this approach is very repetitive. Is there any better way to do this and can someone explain why file array is logging undefined on the console

Answer 1

I would suggest using a recursive approach, this is normally the easiest way to proceed with this kind of problem. The code below should accomplish what you wish. The server will respond with a list of files in the specified folder:
const fs = require('fs');
const path = require('path');
const { promisify } = require('util');
const getStats = promisify(fs.stat);
const readdir = promisify(fs.readdir);
const http = require('http');
handle_files = async (req, res) => {
let files = await scanDir("logs_of_109");
console.log(`Scan complete, file count: ${files.length}`);
res.writeHead(200, {'Content-Type': 'text/plain'});
res.write(files.join(", "));
res.end();
};
http.createServer(handle_files).listen(8080)
async function scanDir(dir, includeDirectories = false, fileList = []) {
let files = await readdir(dir);
for(let file of files) {
let filePath = path.join(dir, file);
try {
let stats = await getStats(filePath);
let isDirectory = stats.isDirectory();
if (includeDirectories || !isDirectory) {
fileList.push(filePath);
}
if (stats.isDirectory()) {
await scanDir(filePath, fileList);
}
} catch (err) {
// Drop on the floor..
}
}
return fileList;
}