Getting User Input in Node.js
Getting User Input in Node.js
Synchronous Input
Node.jsallows you to runJavaScriptcode 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 runningasynchronously, which means that reading user input from a terminal isn’t as simple as calling agetInput()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-inprocessobject andreadlinemodule. While these are powerful tools, they rely oncallback functionsand 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();});
Copy to clipboardconst 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.jsWho are you?>
Copy to clipboard$ node read.jsWho are you?>Then you could enter your input based on the prompt and see the response:
$ node read.jsWho are you?> CodecademyHey there Codecademy!$
Copy to clipboard$ node read.jsWho are you?> CodecademyHey there Codecademy!$This works as intended, but it’s a lot of boilerplate, and you need to callreadline.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.
Usingprompt-sync
Theprompt-syncNode moduleprovides an easy-to-use alternative to this callback-based syntax.
- Make sure you have Node and NPM installed
- Runnpm install prompt-syncin the terminal
const prompt = require('prompt-sync')();
Copy to clipboardconst prompt = require('prompt-sync')();Notice the extra()afterrequire(). Theprompt-syncmodule is a function that creates prompting functions, so you need to callprompt-syncin order to get your actual prompting function.
Once you’ve loaded theprompt-syncmodule 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}`);
Copy to clipboardconst prompt = require('prompt-sync')();
const name = prompt('What is your name?');console.log(`Hey there ${name}`);Theprompt()function returns the user feedback, so simply store that return value to a variable to use it later. In the example above, thenamevariable 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 withCtrl+C(This sends aSIGINT, or “signal interrupt” message indicating that a user wants to exit a program). Withprompt-sync, in order to make sure that your users can exit at will, add a configuration object withsigint: truewhen invoking theprompt-syncfunction:
const prompt = require('prompt-sync')({sigint: true});
Copy to clipboardconst 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);
Copy to clipboardconst 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 - 10const numberToGuess = Math.floor(Math.random() * 10) + 1;// This variable is used to determine if the app should continue prompting the user for inputlet 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!'); }}
Copy to clipboardconst prompt = require('prompt-sync')({sigint: true});
// Random number from 1 - 10const numberToGuess = Math.floor(Math.random() * 10) + 1;// This variable is used to determine if the app should continue prompting the user for inputlet 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!'); }}'The Codecademy Team, composed of experienced educators and tech experts, is dedicated to making tech skills accessible to all. We empower learners worldwide with expert-reviewed content that develops and enhances the technical skills needed to advance and succeed in their careers.'
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