Read files from folders inside a folder - node.js

Question

So basically I have a folder, which holds other folders and each folder has it's own set of images, that I would like to display in a 'ul'. The problem is since I'm using readdir, which is async, how can I write the response, without getting a "Write after .end() error". Here is how my code looks like.
var fs = require('fs'),
url = require('url');
module.exports = function(req, res) {
req.pathName = req.pathName || url.parse(req.url).pathname;
if(req.pathName === '/gallery') {
fs.readdir('./content/images/public', function(err, filenames) {
if (err) {
console.log(err);
return;
}
if(filenames.length) {
var list_content = '';
for (var i = 0; i < filenames.length; i++) {
fs.readdir('./content/images/public/' + filenames[i], function(err, images) {
if (err) {
console.log(err);
return;
}
for (var i = 0; i < images.length; i++) {
list_content += '<li>' + images[i] + '</li>';
}
var list = '<ul>' + list_content + '</ul>Go back to homepage';
res.writeHead(200, {
'Content-Type': 'text/html'
});
res.send(list);
});
}
} else {
res.writeHead(200, {
'Content-Type': 'text/html'
});
res.write('<p>There are no images in the gallery</p>Go back to homepage');
res.end();
}
});
} else {
return true;
}
}
res.end();
}
});

Answer 1

Instead of using res.write() and res.end(), try using res.send(), which does both for you. UPDATE: Also, make sure this code is within a request callback where req, and res object is parsed correctly.
for (var i = 0; i < images.length; i++) {
list_content += '<li>' + images[i] + '</li>';
}
var list = '<ul>' + list_content + '</ul>Go back to homepage';
res.send(list);
then on the front end, receive it in the ajax response callback, like
$.post('xxxx', function(response){
alert(response); //list
});
UPDATE: after seeing your updated code,
module.exports = function(req, res) {
doesnt make sense, it needs to be something like
exports.functionName = function(req,res){
read this
https://www.sitepoint.com/understanding-module-exports-exports-node-js/
module.exports is an object of functions. Not a function. It looks like this
module.exports = {
funcExample: function() {
return 2;
},
funcOtherExample: function() {
return 1;
}