Node.js Readline Introduction

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Every now and then, we need our applications to have a little chit-chat with users. In Node.js, the readline module is the perfect companion for creating interactive command-line interfaces. It allows us to read input from users and display output, making it an essential tool for building communication bridges between our programs and the human world.

Readline Module Overview

The readline module is built into Node.js, which means we don't have to install any additional packages (phew!). To start using it, all we need to do is require the module like this:

const readline = require("readline");

Now that we've got readline in our toolbox, let's explore how to create a simple interface.

Creating a Readline Interface

To create a readline interface, we need to call the createInterface method and pass in an object with the input and output streams. The most common configuration is to use the process.stdin (standard input) and process.stdout (standard output) streams, like so:

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

With our shiny new readline interface (rl), we can now easily ask questions and receive answers from the user.

Asking Questions and Reading User Input

To ask a question, we use the question method on our readline interface. This method takes two arguments: the question text and a callback function that will be executed when the user provides an answer. The user's answer will be passed to the callback as its first argument. Here's an example:

rl.question("What's your favorite programming language? ", (answer) => {
    console.log(`Ah, so you like ${answer}!`);
    rl.close();
});

When the user types their answer and hits Enter, the callback function will be called, and we'll display the response using console.log. Don't forget to close the interface with rl.close() when you're done!

Wrapping It Up

Now you know how to create a readline interface in Node.js and communicate with users through questions and answers. With this newfound knowledge, you're ready to create engaging command-line applications that interact with users in a smooth, natural way. So go on, start a conversation with your code and see where it takes you!

FAQ

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

rl.question("What's your name? ", (answer) => {
    console.log(`Hello, ${answer}!`);
    rl.close();
});

const fs = require("fs");
const readline = require("readline");
const fileStream = fs.createReadStream("example.txt");
const rl = readline.createInterface({
    input: fileStream,
    output: process.stdout
});
rl.on("line", (line) => {
    console.log(`Line from file: ${line}`);
});