How to request user input in Node.js?

Question

I’m having trouble using the function prompt on Node.js. I intend to receive the value a user wants for verification and resolution of my code. But, when running the code, I get this error:

ReferenceError: prompt is not define

My code is:

var distance = prompt("Digite aqui a distância");

if (distance >= 6 && distance <= 800008) {
    console.log("distância aprovada");
}

If it is not possible to use the function prompt, which can replace?

Answer 1

Unlike browsers, exposing a function in the global object called prompt, Node.js does not implement it.

To request a user input, you can use the module readline, from Node.js. See an example:

const readline = require('readline');

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

rl.question('Qual o seu nome? ', (name) => {
  console.log(`Olá, ${name}!`);
});

Note that, unlike prompt, which is synchronous in browsers (and blocks the Event loop), the method question is asynchronous.

You can also convert this method to the promise interface using the function promisify, available in the module util. Thus:

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

// Utilize `question` com a interface de promessas...
const question = promisify(rl.question).bind(rl);

^{Note that I have omitted the definition of rl, which has already been demonstrated in the first example.}

---

One curiosity is that the Deno, unlike Node.js, implements prompt (see here). This is probably due to the fact that Deno attaches great importance to maintaining greater compatibility with the standards already established on the web.