Node.js Readline Module

Introduction to the Readline Module

It's particularly useful for:

Common Use Cases

Interactive command-line applications

Configuration wizards and setup tools

Command-line games

REPL (Read - Eval - Print Loop) environments

Processing large text files line by line

Building custom shells and CLIs

Key Features

Line-by-line input processing

Customizable prompts and formatting

Tab completion support

History management

Event-driven interface

Promise-based API support

Note:

Getting Started with Readline

Here's a quick example of using the Readline module to create a simple interactive command - line application:

Basic Interactive Prompt const readline = require('readline');
// Create interface for input/output const rl = readline.createInterface({

});
// Ask a question and handle the response rl.question('What is your name? ', (name) => {
console.log(`Hello, ${name}!`);
// Ask follow-up question rl.question('How old are you? ', (age) => {
console.log(`In 5 years, you'll be ${parseInt(age) + 5} years old.`);
// Close the interface when done rl.close();
});
});
// Handle application exit rl.on('close', () => {
console.log('Goodbye!');
process.exit(0);
});

Importing and Setup

// Basic require const readline = require('readline');
// Import specific methods using destructuring const { createInterface } = require('readline');
// Create interface with default settings const rl = createInterface({

});
ES Modules (Node.js 12+)
// Using default import import readline from 'readline';
// Using named imports import { createInterface } from 'readline';
// Dynamic import (Node.js 14+)
const { createInterface } = await import('readline');
// Create interface const rl = createInterface({

});

Best Practice:

Creating a Readline Interface

Basic Interface Creation const readline = require('readline');
// Create a basic interface const rl = readline.createInterface({
input: process.stdin,    // Readable stream to listen to output: process.stdout,   // Writable stream to write to prompt: '> ',             // Prompt to display (default: '> ')
});

Common Options:

output

: Optional function for tab auto - completion crlfDelay

Advanced Interface Example

const readline = require('readline');
const fs = require('fs');
// Create an interface with advanced options const rl = readline.createInterface({
input: fs.createReadStream('input.txt'),  // Read from file output: process.stdout,                  // Write to console terminal: false,                         // Input is not a terminal historySize: 100,                        // Larger history removeHistoryDuplicates: true,           // Don't store duplicate commands prompt: 'CLI> ',                         // Custom prompt crlfDelay: Infinity,                     // Handle all CR/LF as single line break escapeCodeTimeout: 200                   // Faster escape code detection
});
// Handle each line from the file rl.on('line', (line) => {
console.log(`Processing: ${line}`);
});
// Handle end of file rl.on('close', () => {
console.log('Finished processing file');
});

Note: