Node always returns empty array

Question

I have the following Get request in server...

var imageFiles = [];
var dir = 'public/img/';
fs.readdir(dir, function(err, files){
    if (err) return console.error(err);
    files.forEach(function(file) {
            file = dir + file;
            imageFiles.push(file)
    });
});
res.send(imageFiles);
res.end();

imageFiles always returns to angular as an empty array. If I console.log(imageFiles) before the response it is empty as well. However, if I console.log(files) they are all there. What am I doing wrong!?

You are sending the response before the directory was traversed. readdir is asynchronous. Send the response inside the callback. — Felix Kling
– Felix Kling, Commented Mar 28, 2014 at 0:34
If you're going to use NodeJS, you're really going to need to spend some time learning about async programming. — cookie monster
– cookie monster, Commented Mar 28, 2014 at 0:34

bryanmac · Accepted Answer · 2014-03-28 00:34:46Z

0

fs.readdir is an async function. It completes in the callback function passing files.

So, when you do res.send, images files is empty.

var imageFiles = [];
...
fs.readdir(dir, function(err, files){
    // files is populated here after readdir returns.
});

// this line executes before readdir returns
res.send(imageFiles);

You need to do something like:

var imageFiles = [];
...
fs.readdir(dir, function(err, files){
    ...
    res.send(imageFiles);
    res.end();
});

Welcome to async programming :)

Checkout async.js. It helps untangle callback hell:

http://www.sebastianseilund.com/nodejs-async-in-practice

answered Mar 28, 2014 at 0:34

bryanmac

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2 Comments

aedballs Over a year ago

Thank you very much! I knew it was async and feel stupid for not thinking of that... I'll mark this as the answer as soon as I can.

bryanmac Over a year ago

np - takes some getting used to.

Ryan · Accepted Answer · 2014-03-28 00:42:02Z

0

Since Array.prototype.forEach is blocking, you can just call your other methods after the foreEach statement. ;

fs.readdir(dir, function(err, files){
    if (err) return console.error(err);
    files.forEach(function(file) {
            file = dir + file;
            imageFiles.push(file)
    });
    res.send(imageFiles);
    res.end();
});

answered Mar 28, 2014 at 0:42

Ryan

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