Getting User Input in Node.js

Synchronous Input

Node.js allows you to run JavaScript code outside of a browser window, offering powerful tools to interact with a computer filesystem, run web servers, and create terminal applications. Node handles these tasks by running asynchronously, which means that reading user input from a terminal isn’t as simple as calling a getInput() function. In this article, we’ll show you an easy way around that (and some tips and tricks for handling user input) by using a helpful Node module.

Working with Input

Node.js provides a few ways to handle interactions, including the built-in process object and readline module. While these are powerful tools, they rely on callback functions and can be confusing to work with at first.

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

readline.question('Who are you?', name => {
  console.log(`Hey there ${name}!`);
  readline.close();
});

Running this code in Node, you’d see:

$ node read.js
Who are you?
> 

Then you could enter your input based on the prompt and see the response:

$ node read.js
Who are you?
> Codecademy
Hey there Codecademy!
$

This works as intended, but it’s a lot of boilerplate, and you need to call readline.question() and create a callback function every time you want to use it for input. There’s a simpler way, whether you’re just getting started out with JavaScript development or just want to get an interactive script running as quickly as possible.

Using prompt-sync

The prompt-sync Node module provides an easy-to-use alternative to this callback-based syntax.

1. Make sure you have Node and NPM installed
2. Run npm install prompt-sync in the terminal

const prompt = require('prompt-sync')();

Notice the extra () after require(). The prompt-sync module is a function that creates prompting functions, so you need to call prompt-sync in order to get your actual prompting function.

Once you’ve loaded the prompt-sync module and called it, using it to retrieve user input is relatively straightforward:

const prompt = require('prompt-sync')();

const name = prompt('What is your name?');
console.log(`Hey there ${name}`);

The prompt() function returns the user feedback, so simply store that return value to a variable to use it later. In the example above, the name variable stores the value, and it is then repeated to the user on the next line.

Letting Users Exit

By default, most terminal programs will exit with Ctrl + C (This sends a SIGINT, or “signal interrupt” message indicating that a user wants to exit a program). With prompt-sync, in order to make sure that your users can exit at will, add a configuration object with sigint: true when invoking the prompt-sync function:

const prompt = require('prompt-sync')({sigint: true});

Working with Numbers

All user input will be read as a String, so in order to treat user input as numbers, you’ll need to convert the input:

const num = prompt('Enter a number: ');
console.log('Your number + 4 =');
console.log(Number(num) + 4);

Making a basic app

The code below creates a small number guessing application.

const prompt = require('prompt-sync')({sigint: true});

// Random number from 1 - 10
const numberToGuess = Math.floor(Math.random() * 10) + 1;
// This variable is used to determine if the app should continue prompting the user for input
let foundCorrectNumber = false;

while (!foundCorrectNumber) {
  // Get user input
  let guess = prompt('Guess a number from 1 to 10: ');
  // Convert the string input to a number
  guess = Number(guess);

  // Compare the guess to the secret answer and let the user know.
  if (guess === numberToGuess) {
    console.log('Congrats, you got it!');
    foundCorrectNumber = true;
  } else {
    console.log('Sorry, guess again!');
  }
}