For-loop and async callback in node.js?

Question

I\'m new to JavaScript and to node.js. I want to loop through a directory and add all file stat (not other directories) to an array. As you see below there is a problem with

Answer 1

Alternatively use the new threads module ( https://github.com/robtweed/Q-Oper8 ) and then you can do all this stuff much more simply using standard synchronous coding within the threads child processes, since they only deal with one user's request at a time.

Goodbye to async logic and nested callbacks!

Answer 2

One way is to rewrite the innards of the loop to use a closure:

fs.readdir(SYNCDIR, function(err1, files) {
    var filesOnly = [];
    if(!err1) {
        for(var i = 0; i < files.length; i++) {
            (function(index) {
                var imgFilePath = SYNCDIR + '/' + files[index];
                fs.stat(imgFilePath, function(stat){
                    if (stat.isFile()){
                        filesOnly[index] = stat;
                    }
                });
            })(i);
        }
    }
});

A better looking example, achieving the same, using Array.prototype.forEach:

fs.readdir(SYNCDIR, function(err1, files) {
    var filesOnly = [];
    if(!err1) {
        files.forEach(function(file, i) {
            var imgFilePath = SYNCDIR + '/' + file;
            fs.stat(imgFilePath, function(stat){
                if (stat.isFile()){
                    filesOnly[i] = stat;
                }
            });
        });
    }
});

Answer 3

You are right about needing to use a closure. You should wrap the contents of the for loop in a self-invoking function to preserve the value of i for each iteration.

fs.readdir(SYNCDIR, function(err1, files) {
    var filesOnly = [];

    if(!err1) {

        for(var i = 0; i < files.length; i++) {

            (function(i) {
                var imgFilePath = SYNCDIR + '/' + files[i];
                fs.stat(imgFilePath, function(stat){
                    if (stat.isFile()){
                        filesOnly[i] = stat;
                    }
                });
            })(i);

        }
    }
});