`util.promisify` for `readline.question`

promisify-readline-question.js

'use strict';

// Promisifies readline.question function using node native `util.promisify`
// readline.question takes one callback that returns the answer, so it need custom promisifying

const readline = require('readline');
const { promisify } = require('util');

readline.Interface.prototype.question[promisify.custom] = function(prompt) {
  return new Promise(resolve =>
    readline.Interface.prototype.question.call(this, prompt, resolve),
  );
};
readline.Interface.prototype.questionAsync = promisify(
  readline.Interface.prototype.question,
);

/* Usage example then:
(async () => {
    const rl = readline.createInterface({
      input: process.stdin,
      output: process.stdout,
    });

    const airportCode = await rl.questionAsync(
      'Enter the airport code for stats: ',
    );
    rl.close();
    console.info('Getting stats for %s...', airportCode);
})();
*/

Thanks for the code! I found another to do the same thing, I thought I'd share:

const readline = require('readline');
const { promisify } = require('util');
const readline = readline.createInterface({
      input: process.stdin,
      output: process.stdout,
    });

// Prepare readline.question for promisification
readline.question[util.promisify.custom] = (question) => {
  return new Promise((resolve) => {
    readline.question(question, resolve);
  });
};

// Usage example:
const answer = await promisify(readline.question)('What is your name? ');
readline.close();
console.log('Hi %s!', answer);

I really doubt this code could run. You're reassigning a const. And doing many other strange things. Did you just copy-paste random code?

I really doubt this code could run. You're reassigning a const. And doing many other strange things. Did you just copy-paste random code?

The base idea works, it was just untested, so heres the tested version:

const { promisify } = require('util');
const readline = require("readline");
let rl = readline.createInterface({ input: process.stdin, output: process.stdout });

rl.question[promisify.custom] = (question) => {
    return new Promise((resolve) => {
      rl.question(question, resolve);
    });
};
rl.questionSync = promisify(rl.question);

runAsync();
async function runAsync() {
    let ans = await rl.questionSync("What is your name ?\n");
    console.log(ans);
}

Wow, that's a collection of antipatterns. Anyway, promisified version is landed in Node 16