Node JS : Reading input from readable streams : readline

Understanding the Readline Module

The readline module in Node.js is designed to read data from a readable stream, such as process.stdin, one line at a time. It’s especially handy for creating command-line interfaces (CLIs) or reading large files without loading them entirely into memory.

Key Features

  • Line-by-Line Reading: Efficiently process data one line at a time.
  • Event-Driven: Leverages Node.js’s event-driven architecture.
  • Customizable Interfaces: Allows for tailored input and output streams.

Before diving into the example, ensure you have Node.js installed. You can check this by running node -v in your terminal. If you don’t have Node.js installed, download it from the official Node.js website.

Example: Building a CLI quiz app

In this example, we’ll create a simple CLI quiz application using the readline module. This app will ask users a series of questions and provide immediate feedback.

Step 1: Initialize the readline interface

First, import the readline module and set up the interface.

const readline = require('readline');

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

Step 2: Define the questions and logic

Let’s define a few quiz questions and the logic to process user responses.

const questions = [
  { query: "What is 2 + 2?", answer: "4" },
  { query: "Name the largest planet in our solar system.", answer: "Jupiter" },
  // Add more questions as needed

let currentQuestion = 0;

function askQuestion() {
  rl.question(questions[currentQuestion].query + ' ', (userInput) => {
    if (userInput.trim() === questions[currentQuestion].answer) {
    } else {
      console.log("Incorrect. The correct answer is:", questions[currentQuestion].answer);

    if (currentQuestion < questions.length) {
    } else {

Step 3: Start the quiz

Finally, kick off the quiz by calling askQuestion().


Step 4: Testing the application

Run your Node.js application by navigating to the directory containing your script and running node <script-name>.js. Answer the questions to see how the application responds.

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Author: user