JavaScript Tutorial
Your first JavaScript program teaches the full input → logic → output flow.
Start simple with console.log, then expand into variables, conditions, and reusable logic.
This first program builds confidence and the mental model for how JavaScript executes.
It also sets the foundation for functions, loops, and real-world apps.
console.log("Hello, World!");
const name = "Asha";
if (name) { console.log(name); }console.log("Hello, World!");console.log() prints text to the console. This is your first output.
console.log("Hello from the console!");
const message = "Test";
console.log(message);Use DevTools Console for instant feedback while learning.
A JavaScript program is a sequence of instructions executed by the JavaScript engine.
Programs follow a simple pattern: accept input → process logic → produce output.
Your first program will be simple, but it demonstrates all the fundamentals of how code execution works.
As you progress, programs become more complex by combining multiple concepts together.
Traditionally, the first program prints "Hello, World!" to demonstrate that code can execute.
In JavaScript, console.log() is the built-in function for printing output.
console is an object, log() is a method, and the text in quotes is the content to print.
This single line demonstrates variables, strings, objects, methods, and output.
The fastest way to run JavaScript is directly in your browser's DevTools Console.
No files needed, no setup required - just open the console and type.
Perfect for learning, testing snippets, and debugging.
Every modern browser (Chrome, Firefox, Safari, Edge) has built-in DevTools.
To run more complex programs, create an HTML file with embedded JavaScript.
The <script> tag contains your JavaScript code.
Opening the file in a browser executes the script.
Use DevTools Console to see console.log() output.
Professional projects separate HTML and JavaScript into different files.
Create a separate .js file and link it in HTML using <script src="file.js"></script>.
This approach scales better for larger applications.
Makes code reusable and testing easier.
Node.js is a JavaScript runtime that executes JavaScript outside the browser.
Perfect for running scripts, building servers, and automating tasks.
Install Node.js, create a .js file, and run it with node filename.js.
Useful for backend development and command-line tools.
Combine what you've learned to create a program that actually does something.
Use variables to store data, console.log() to print output, and conditional logic to make decisions.
This program could greet a user, calculate values, or validate input.
JavaScript executes code line by line from top to bottom.
Variables are created when declared and remembered for the rest of the program.
Each statement completes before the next one starts.
Understanding execution order is crucial for debugging and learning.
Typos in variable and function names cause errors.
Forgetting quotes around strings breaks the program.
JavaScript is case-sensitive - "name" and "Name" are different.
Mismatched parentheses or brackets prevent execution.
<!-- index.html -->
<!DOCTYPE html>
<html>
<body>
<script src="script.js"></script>
</body>
</html>
// script.js
console.log("External JavaScript file loaded!");Separating files is the professional standard for maintainable projects.
// app.js
console.log("Running in Node.js!");
const sum = 5 + 3;
console.log(`5 + 3 = ${sum}`);
// Run: node app.jsNode.js lets you run JavaScript outside the browser.
const userName = "Sarah";
const userAge = 17;
const currentYear = 2024;
const birthYear = currentYear - userAge;
const isAdult = userAge >= 18;
console.log(`Hello, ${userName}!`);
console.log(`Birth year: ${birthYear}`);
console.log(isAdult ? "Adult" : "Minor");Combines variables, template literals, and conditions into one program.
Without
// No output
const name = "Asha";With
// With output
const name = "Asha";
console.log("Hello, " + name);Start with console.log(), simple variables, and basic conditions. Then build up complexity.
Error messages tell you exactly what's wrong. Read them carefully to fix issues quickly.
Print variable values to understand what's happening. Console.log is your best debugging friend.
Keep them separate for cleaner, more maintainable code.
Code runs top-to-bottom. Use the correct variable names after declaration.
It prints output to the console so you can see program results.
Code runs top-to-bottom, one statement at a time.
A sequence of instructions executed by the JavaScript engine.
Practice: Print a greeting with a name and age.
const name = "Riya";
const age = 20;
// TODO: print greeting with name and age
One Possible Solution
const name = "Riya";
const age = 20;
console.log(`Hello, ${name}. You are ${age} years old.`);Console is immediate and interactive for testing. Files persist code and are used for actual programs. Both execute the same way.
Core JavaScript can run in both, but Node.js-specific APIs (file system, process) don't work in browsers.
Start with console for quick experimentation. Move to HTML files for interactive programs. Use Node.js once you understand basics.
No. Browser console needs nothing. For Node.js, install from nodejs.org. For files, just use a text editor.
Check the error message. Use console.log() to print variable values. Open DevTools console to see what's happening.
Learn variables, data types, operators, conditions, loops, functions, and objects - in that order.
In HTML, link multiple scripts. In Node.js, use require() or import. In console, each line is independent.
No. Professional developers use console.log() constantly for debugging and monitoring programs.
Run the classic Hello World example and then change the text.