Example FTP script that connects to an FTP server, lists the directory's files, chooses one to download, renames it locally, then re-uploads it.

example-ftp.js

import fs from "fs";
import { fileURLToPath } from "url";
import {join, parse, dirname} from "path";
import FtpClient from "ftp";

const FTP_READY_EVENT = "ready";
const FS_CLOSE_EVENT = "close";

const config = { // See https://www.npmjs.com/package/ftp#methods.
  host: "ftp.dlptest.com",
  user: "dlpuser", // Courtesy of https://dlptest.com/ftp-test/
  password: "rNrKYTX9g7z3RgJRmxWuGHbeu",
  path: "",
}

const localDownloadsDir = join(dirname(fileURLToPath(import.meta.url)), "UNSAFE_DOWNLOADS/"); // https://stackoverflow.com/a/62892482/1862046

const ftpClient = new FtpClient();
ftpClient.on(FTP_READY_EVENT, () => {

  ftpClient.list(config.path, (listErr, fileInfos) => {
    if (listErr) throw listErr;
    console.dir(fileInfos);
    console.log("Found", fileInfos.length, "files");

    const fileInfo = fileInfos.find(({name, rights, size}) => size > 0 && /\.(json)$/i.test(name) && rights.other.includes('r'));
    if (!fileInfo) { console.warn("No file found;"); ftpClient.end(); return; }
    console.log("Found suitable file:", fileInfo.name, {size: fileInfo.size, ...fileInfo.rights});

    ftpClient.get(fileInfo.name, function(fileErr, fileStream) {
      if (fileErr) throw fileErr;
      console.log("Downloading", fileInfo.name, "to", localDownloadsDir);

      const iteration = fileInfos.reduce((max, {name}) => Math.max(max, (name.match(/_v(\d+)\.[a-z]+$/) || [])[1] || 0), 0) + 1
      const localFilepath = join(localDownloadsDir, `${parse(fileInfo.name).name}_v${iteration}${parse(fileInfo.name).ext}`);
      fileStream.pipe(fs.createWriteStream(localFilepath));
      fileStream.once(FS_CLOSE_EVENT, () => {
        console.log("Download finished.");

        const remoteFilename = `${parse(fileInfo.name).name}_v${iteration+1}${parse(fileInfo.name).ext}`;
        console.log("Uploading", remoteFilename);

        ftpClient.put(localFilepath, remoteFilename, (uploadErr) => {
          if (uploadErr) throw uploadErr;
          console.log("Upload finished; disconnecting.");
          ftpClient.end();
        });
      });
    });
  });
});

ftpClient.connect(config);