local variable is not changing - node.js

Question

I'm using node.js for converting text files to CSV. It works for one file, but when i try process more files fileDestination variable doesn't change. Why? Input files like this: r10_1C_BP1-11_e41-81_10_5X1x9_05_train2.res
I got following console output:
./1_train.csv has been written successufully! r10_1C_BP1-11_e41-81_10_5X1x9_05_train2.res
./1_train.csv has been written successufully! r10_1C_BP1-11_e41-81_1_5X1x9_05_train2.res
/*
* lee archivos *.dat y los convierte *.csv
*/
const fs = require('fs');
const inputDir = './';
const outputDir = './';
function readFiles(inputDir, onError) {
fs.readdir(inputDir, function(err, filenames) {
if (err) {
onError(err);
return;
}
filenames.forEach(function(inputFile) {
// first we arre looking for "right" file name
if (inputFile.search(/res/) != -1) {
console.log('Starting processing ' + inputFile);
convert2csv(inputFile, function(error) {
throw err;
});
}
});
});
}
function convert2csv(filename, onError) {
arrayFromFilename = filename.split('_');
epoca = arrayFromFilename[4];
trainORval = arrayFromFilename[7].replace('2.res', '');
console.log("from convert " + filename + " " + epoca);
fs.readFile(inputDir + filename, 'utf-8', function(err, content) {
if (err) {
onError(err);
return;
}
content = content.replace(/^[^0].*\n/mg, '');
arr = content.split('\n');
pares = arr.filter(function(d, i) {
return i % 2 == 1;
});
content = pares.join('\n');
content = content.replace(/(^[\d.]*) ([\d.]*)/gm, '$1,$2');
fileDestination = outputDir + epoca + '_' + trainORval + '.csv';
console.log("filedestination :" + fileDestination);
fs.writeFile(fileDestination, 'y,x\n', function(err) {
if (err) {
return console.error(err);
}
fs.appendFile(fileDestination, content, function(err) {
if (err) {
return console.error(err);
}
console.log(fileDestination + " has been written successufully!", filename);
});
});
});
}