combine csv files javascript

                                    const file1 = 'one.csv';
const file2 = 'two.csv';
const stream = fs.createReadStream(file1);
const stream2 = fs.createReadStream(file2);
const fileData1 = [];
const fileData2 = [];

const file1Promise = new Promise((resolve) => {
  csv
      .parseFile(file1, {headers: true})
      .on('data', function(data) {
        fileData1.push(data);
      })
      .on('end', function() {
        console.log('done');
        resolve();
      });
});

const file2Promise = new Promise((resolve) => {
  csv
      .parseFile(file2, {headers: true})
      .on('data', function(data) {
        fileData2.push(data);
      })
      .on('end', function() {
        console.log('done');
        resolve();
      });
});

Promise.all([
  file1Promise,
  file2Promise,
])
    .then(() => {
      const fileData3 = fileData1.concat(fileData2);
      console.log(fileData3);

      const csvStream = csv.format({headers: true});
      const writableStream = fs.createWriteStream('outputfile.csv');

      writableStream.on('finish', function() {
        console.log('DONE!');
      });

      csvStream.pipe(writableStream);
      fileData3.forEach((data) => {
        csvStream.write(data);
      });
      csvStream.end();
    });

                                    function JSON2CSV(objArray) {
    var array = typeof objArray != 'object' ? JSON.parse(objArray) : objArray;
    var str = '';
    var line = '';

    if ($("#labels").is(':checked')) {
        var head = array[0];
        if ($("#quote").is(':checked')) {
            for (var index in array[0]) {
                var value = index + "";
                line += '"' + value.replace(/"/g, '""') + '",';
            }
        } else {
            for (var index in array[0]) {
                line += index + ',';
            }
        }

        line = line.slice(0, -1);
        str += line + '\r\n';
    }

    for (var i = 0; i < array.length; i++) {
        var line = '';

        if ($("#quote").is(':checked')) {
            for (var index in array[i]) {
                var value = array[i][index] + "";
                line += '"' + value.replace(/"/g, '""') + '",';
            }
        } else {
            for (var index in array[i]) {
                line += array[i][index] + ',';
            }
        }

        line = line.slice(0, -1);
        str += line + '\r\n';
    }
    return str;
}

                                    var file1 = appRoot + '\\csvFiles\\details1.csv';
var file2 = appRoot + '\\csvFiles\\idetails2.csv';
var stream = fs.createReadStream(file1);
var stream2 = fs.createReadStream(file2);
var fileData1 = [],
    fileData2 = [],
    i = 0;

csv.fromStream(stream).on("data", function(data) {
    fileData1.push(data);
}).on("end", function() {
    csv.fromStream(stream2).on("data", function(data) {
        if (i != 0) {
            fileData2.push(data);
        }
        i++;
    }).on("end", function() {
        console.log("done");
        var fileData3 = fileData1.concat(fileData2);
        csv.writeToPath("outputfile.csv", fileData3).on("finish", function() {
            res.send('Done merge');
        });
    });
});