Export CSV without crash from node js - node.js

Question

I need to export CSV for large amount of data, like it's having 100k rows, I'm using Json2CSV but sometimes it's taking a long time and crashed. I'm using node js stream but no use. I am googling but I don't have idea to clear it.Please any one can guide me how can I fix it.
Node JS
var formatedData = {......} //object with data
let filename = 'test' + '.csv';
let pathName = await writeToCSV(filename, formatedData, fields);
let readStream = fs.createReadStream(pathName);
res.setHeader('Content-disposition', `attachment; filename=${filename}`);
res.set('Content-Type', 'text/csv');
let downloadStream = readStream.pipe(res);
fields = null;
formatedData = null;
downloadStream.on('finish', function() {
fs.unlink(pathName, function() {});
downloadStream = null;
readStream = null;
});
writeToCSV
function writeToCSV(filename, data, fields, option) {
return new Promise((resolve, reject) => {
if (typeof data !== 'object') {
return reject(new Error('Data is not an object'));
}
let options = {
fields
};
if (typeof option === 'object') {
for (let key in option) {
options[key] = option[key];
}
}
let tmpPath = path.join(__dirname, '..', tmp);
let pathFile = tmpPath + filename;
return Promise.all([Promise.resolve(json2csv(data, options).split('\n')), checkTMPExist(tmpPath)]).then(data => {
let csvFormat = data[0];
let writeStream = fs.createWriteStream(pathFile);
csvFormat.forEach((lines, index) => {
if (index === csvFormat.length - 1) {
writeStream.end(lines + '\n');
} else {
writeStream.write(lines + '\n');
}
});
writeStream.on('finish', function() {
this.end();
return resolve(pathFile);
});
writeStream.on('error', function(err) {
this.end();
fs.unlink(pathFile, () => {});
return reject(err);
});
}).catch(err => {
fs.unlink(pathFile, () => {});
return reject(err);
});
});
}
Front end Ajax call
function export_csv(url, fileName) {
$.ajax({
url: url,
type: "GET",
success: function (result) {
var encodedUri = 'data:application/csv;charset=utf-8,' + encodeURIComponent(result);
var link = document.createElement("a");
link.setAttribute("href", encodedUri);
link.setAttribute("download", fileName);
document.body.appendChild(link);
link.click();
},
error: function (xhr) {
console.log("Export csv have some issue:" + JSON.stringify(xhr));
}
});
}