Skip to main content

Hello World (Console)

The simplest possible program

Overview​

This is your first program. It does one thing: prints "Hello, World!" to the console.

Why start here?

  • Demonstrates what a program is (instructions that execute)
  • Shows input → processing → output at the simplest level
  • Introduces running code from the command line
  • No abstractions, no frameworks — just pure fundamentals

Time to complete: 10-15 minutes

What You'll Learn​

  • What a program is and how it runs
  • How to execute JavaScript with Node.js
  • Basic syntax: functions, strings, console output
  • The concept of an entry point

Prerequisites​

  • Node.js installed (check with node --version)
  • A terminal or command prompt
  • A text editor (VS Code recommended)

The Code​

File: hello.js

// This is a comment — it doesn't run, just explains code

// Define a function that prints a greeting
function sayHello() {
  console.log("Hello, World!");
}

// Call the function (this makes it run)
sayHello();

That's it. 6 lines of actual code.

How to Run​

  1. Open a terminal
  2. Navigate to this directory: 
    cd examples/00-hello-world-console
  3. Run the program: 
    node hello.js
  4. You should see: 
    Hello, World!

Understanding the Code​

Line by Line​

// This is a comment

Comments are notes for humans. The computer ignores them.

function sayHello() {

This defines a function named sayHello. Think of it as creating a recipe.

  console.log("Hello, World!");

This is the body of the function. console.log() prints text to the terminal.

}

This closes the function definition.

sayHello();

This calls the function. Without this line, nothing would happen (the recipe exists, but you haven't cooked it).

Key Concepts​

1. Programs are Instructions​

A program is a series of instructions the computer follows, step by step.

2. Functions are Reusable Recipes​

A function is a named block of code you can run multiple times.

Example:

function sayHello() {
  console.log("Hello, World!");
}

sayHello();  // Prints: Hello, World!
sayHello();  // Prints: Hello, World!
sayHello();  // Prints: Hello, World!

3. Entry Point​

When you run node hello.js, Node.js starts at the top of the file and executes each line in order.

Architectural Views​

Even this tiny program can be viewed architecturally!

Module View (Static Structure)​

What this shows: A single file, executed by Node.js.

Component-Connector View (Runtime Behavior)​

What this shows: The flow of execution from start to finish.

Allocation View (Deployment)​

What this shows: Everything happens on your local computer in the terminal.

Exercises​

Exercise 1: Modify the Message​

Change "Hello, World!" to "Hello, [YourName]!" and run again.

Expected output:

Hello, Alice!

Exercise 2: Add Another Function​

Create a new function sayGoodbye() that prints "Goodbye, World!" and call it after sayHello().

Expected output:

Hello, World!
Goodbye, World!

Exercise 3: Add Parameters​

Modify sayHello to accept a name:

function sayHello(name) {
  console.log("Hello, " + name + "!");
}

sayHello("Alice");
sayHello("Bob");

Expected output:

Hello, Alice!
Hello, Bob!

Exercise 4: Input → Processing → Output​

Modify the program to show all three phases:

// INPUT
const name = "Alice";

// PROCESSING
const greeting = "Hello, " + name + "!";

// OUTPUT
console.log(greeting);

Common Issues​

"node: command not found"​

Problem: Node.js is not installed or not in your PATH.

Solution: Install Node.js from nodejs.org

"Cannot find module"​

Problem: You're in the wrong directory.

Solution: Use cd to navigate to the directory containing hello.js.

Nothing prints​

Problem: You forgot to call sayHello().

Solution: Add sayHello(); at the bottom of the file.

Next Steps​

You've created your first program! Now you understand:

  • What a program is
  • How to run JavaScript with Node.js
  • Functions and how to call them
  • The I/O/P model (input, processing, output)

Next: Lemonade CLI — Build a slightly more complex CLI app that takes user input.

Using This Example with AI Assistants​

Prompt Template: Understanding Code​

I'm learning programming with the devfoundry curriculum.
I'm looking at the "Hello World" example (examples/00-hello-world-console).

Here's the code:
[paste hello.js]

Questions:
1. What happens when I run `node hello.js`?
2. What does `console.log()` do?
3. Why do we need the parentheses in `sayHello()`?
4. What would happen if I removed the `sayHello();` line at the bottom?

Please explain in beginner-friendly terms.

Prompt Template: Modifying the Example​

I'm working on the "Hello World" example from devfoundry.

Current code:
[paste hello.js]

I want to modify it to:
- Accept a name as input (not hard-coded)
- Print a personalized greeting

Please show me how to modify hello.js to do this.
Explain what changes you made and why.

Reflection​

Before moving on, make sure you can answer:

  1. What is a function?
  2. What does it mean to "call" a function?
  3. What is the role of Node.js in running this program?
  4. Can you draw the flow of execution (start → define → call → output)?

If any of these are unclear, experiment with the code, try the exercises, or ask an AI assistant using the prompt templates above.

You've taken the first step. Everything builds from here.