find_longest.js

const path = require('path');

let longestLine = '';

const queue = ['./src'];
while (queue.length) {
  const dir = queue.shift();
  const files = fs.readdirSync(dir, { withFileTypes: true });
  files.forEach((f) => {
    const name = path.join(dir, f.name);
    if (f.isDirectory()) {
      queue.push(name);
    } else {
      fs.readFileSync(name, 'utf8')
        .split('\n')
        .forEach((line) => {
          if (line.length > longestLine.length) {
            longestLine = line;
          }
        });
    }
  });
}

console.log(longestLine);