PromisifyReadline.js

const readline = require('readline');

var oldCreateIface = readline.createInterface;
readline.createInterface = function() {
  var iface = oldCreateIface.apply(this, arguments);
  
  var oldQuestion = iface.question;
  iface.question = function(question) {
    var promise = Promise.defer();
    oldQuestion.call(this, question, (result)=>{
      promise.resolve(result);
    });
    return promise.promise;
  }
  iface.choose = function(question) {
    return rl.question(question+" [y/n]")
      .then((a) => {
        return a.toLowerCase()=="y";
      })
  }              
  return iface;
}
module.exports = readline;

usage.js

const path = require("path");

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

var path1, path2;

rl.question("What is the first file?")
  .then((name)=>{
    path1 = name;
    return rl.question("What is the second file?");
  })
  .then((name)=>{
    path2 = name;
    console.log("Relative path: ", path.relative(path1, path2));
    process.exit();
  });