Stream: a large text file line-by-line; dir recursively (NodeJS)

by-line-lib.js

const fs = require("fs");
const readline = require("readline");

const byLine = async ({file, handleLine, charset="utf8"}) => {
  return new Promise((done, err) => {
    if (!fs.existsSync(file)) {
      return err(new Error('File not found!'));
    }
    const rl = readline.createInterface({
      input: fs.createReadStream(file, charset),
      output: process.stdout,
      terminal: false,
    });
    rl.on("line", handleLine);
    rl.on("close", done);
  });
};

function handleLine(line) {...}

const file = "~/mydatafile.txt"; // +100GB!! no prob.
await byLine({file, handleLine});

dir-recursive.js

const walker = require("folder-walker");

function handleFile(file) {...}

const baseFolder = "~";
const doneWalkBaseFolder = new Promise((done) => {
  // recursively walk through a directory via a stream
  const stream = walker([baseFolder]);
  stream.on("data", handleFile);
  stream.on("end", done);
});
await doneWalkBaseFolder;