nodejs simple file menu

menu.js

const fs = require('fs');
const path = require('path');
const readline = require('readline');

const cwd = process.cwd();
const rl = readline.createInterface({ input: process.stdin, output: process.stdout });
const files = [];

const filterExtension = null; // ".json"

fs.readdirSync(cwd).forEach(file => {
  if (!filterExtension || file.endsWith(filterExtension)) {
    files.push(file);
  }
});

const killWords = ['quit', 'q', 'exit'];

let fn = {
  "showList": () => {
    let question = `Please select a number? 1-${files.length}\n\n`;

    for (let i = 0; i < files.length; i++) {
      question += `[${i + 1}] ${files[i]}\n`
    }
    question += '\n> ';

    fn.getFile(question);
  },

  "getFile": (question) => {
    rl.question(question, (input) => {
      input = input.toLowerCase();

      if (isNaN(input)) {
        if (killWords.indexOf(input) != -1) {
          console.log('bye.');
          rl.close();
        } else if (input === 'list') {
          fn.showList();
        } else if (input === 'help') {
          fn.showList();
        } else {
          fn.getFile(`Please enter a number (1 - ${files.length}) > `);
        }
      } else {
        let index = Number(input);

        if (input > 0 && input < files.length + 1) {
          fn.action(files[index - 1]);
          rl.close();
        } else {
          fn.getFile(`Invalid number, please enter a number (1 - ${files.length}) > `);
        }
      }
    })
  },

  "action": (file) => {
    file = path.join(cwd, file);

    console.log(`Action on "${file}"`);
  }

}

if (files.length === 0) {
  if (filterExtension) {
    console.log(`No ${filterExtension.replace('.', '')} files present in directory. Copy the ${filterExtension.replace('.', '')} file('s) into \n'${cwd}'`);
  }
  rl.close();
} else {
  if (files.length > 1) {
    fn.showList();
  }
  else {
    // we don't need to ask any questions so, kill the readline tool.
    rl.close();
    fn.action(files[0]);
  }
}