NodeJS - fs.stat() is ignored in a FOR-loop - node.js

Question

I'm trying to loop over a bunch of directories and then try if a file inside that directory exists with NodeJS and fs.stat().
I've got a simple for-loop to loop over the directories and in it the fs.stat() call to check, if "project.xml" inside that particular directory exists. My code looks like this:
for (var i = 0, length = prDirs.length; i < length; i++) {
var path = Config["ProjectDirectory"] + "/" + prDirs[i];
console.log("PATH=" + path);
fs.stat(path + "/project.xml", function (err, stat) {
if (err == null) {
console.log(" => PATH=" + path);
}
})
}
NodeJS loops correctly over the directory, the console.log() outputs all the directories correctly, but the code inside the if inside fs.stat() is not called and runs only once at the end of the loop. My console shows this:
PATH=(...)/PHP
PATH=(...)/Electron
PATH=(...)/testapp
PATH=(...)/Vala
=> PATH=(...)/Vala/project.xml
But the project.xml I'm looking for is in testapp/ not in Vala/ but Vala/ is the last entry in prDirs.
The code above is my latest attempt, I've tried plenty of other variations and one (I appended an else to the if inside fs.stat()) showed me, that fs.stat() actually gets invoked, but only the code inside the if is not running and the code in the else I appended once was running.
Thanks in advance!

Answer 1

fs.stat is an asynchronous i/o function, so its callback will be called only after the main thread is idle, or in your case, only after the for loop is done. Instead of a for loop, I suggest iterating the folder in an asynchronous matter. You can use async.each, async.eachSeries, or implement it yourself.

Answer 2

As #Gil Z mention fs.stat in async. I would suggest to use promises if you want to keep for each loop and make code looks sync.
Here is the example. Works on node v 6.9
"use strict";
const fs = require('fs');
let paths = ["tasks", "aaa", "bbbb"];
//method to get stat data using promises
function checkFileExists(path) {
return new Promise((resolve, reject) => {
fs.stat(path + "/project.xml", (err, res) => {
resolve(err ? "Not found in " + path : " => PATH=" + path);
});
});
}
//create promise array with each directory
let promiseArr = [];
paths.forEach(pathPart => {
let path = process.cwd() + "/" + pathPart;
promiseArr.push(checkFileExists(path));
});
//run all promises and collect results
Promise.all(promiseArr)
.then(reslut => {
console.log(reslut);
})
.catch(e => console.log("Error in promises"));
The above code will log this
[ ' => PATH=/Users/mykolaborysiuk/Sites/circlemedia/syndic-apiManager/tasks',
'Not found in /Users/mykolaborysiuk/Sites/circlemedia/syndic-apiManager/aaa',
'Not found in /Users/mykolaborysiuk/Sites/circlemedia/syndic-apiManager/bbbb' ]
Hope this helps.