REPL for interactive exploration in Node.js - Mini Project: Build & Apply

Interactive Exploration with Node.js REPL

📖 Scenario: You want to explore JavaScript code interactively using Node.js REPL (Read-Eval-Print Loop). This helps you test small code snippets quickly, like a calculator or trying out functions.

🎯 Goal: Build a simple Node.js REPL session setup where you define variables, configure a prompt, and add a custom command to enhance your interactive exploration.

📋 What You'll Learn

Create a variable with initial data inside the REPL session

Set a custom prompt string for the REPL

Add a custom command to the REPL to clear the console

Start the REPL session with the configured settings

💡 Why This Matters

🌍 Real World

Developers use Node.js REPL to quickly test JavaScript code snippets, debug, and explore APIs without writing full programs.

💼 Career

Knowing how to use and customize REPL helps developers prototype code faster and debug interactively, a valuable skill in software development.

1

Create initial data variable

Create a variable called data and assign it the object { count: 0, message: 'Hello REPL' }.

Node.js

# Your code here

Need a hint?

Use const data = { count: 0, message: 'Hello REPL' }; to create the variable.

2

Configure REPL prompt

Create a variable called repl by requiring 'repl' and start the REPL with a prompt string set to 'MyREPL> '.

Node.js

const data = { count: 0, message: 'Hello REPL' };
// Your code here

Need a hint?

Use const repl = require('repl'); and repl.start({ prompt: 'MyREPL> ' }).

3

Add a custom REPL command

Add a custom REPL command called .clear that clears the console by calling console.clear() inside the REPL server instance replServer.

Node.js

const data = { count: 0, message: 'Hello REPL' };
const repl = require('repl');
const replServer = repl.start({ prompt: 'MyREPL> ' });
// Your code here

Need a hint?

Use replServer.defineCommand('clear', { action() { console.clear(); this.displayPrompt(); } }).

4

Expose data variable in REPL context

Assign the data variable to the REPL server context so you can access it interactively by typing data in the REPL.

Node.js

const data = { count: 0, message: 'Hello REPL' };
const repl = require('repl');
const replServer = repl.start({ prompt: 'MyREPL> ' });
replServer.defineCommand('clear', {
  help: 'Clear the console',
  action() {
    console.clear();
    this.displayPrompt();
  }
});
// Your code here

Need a hint?

Use replServer.context.data = data; to expose the variable.