Day 1: The Language of the Web

Welcome to the JavaScript Fundamentals Series. Over the next 10 days, we will transform you from a complete beginner into a capable web developer.

What is JavaScript?

JavaScript (JS) is the programming language that makes websites interactive.

• HTML is the structure (the skeleton).
• CSS is the style (the clothes).
• JavaScript is the logic (the brain/muscles).

Setting Up

You don’t need to install anything to start! every web browser has a JavaScript engine built-in. However, for this course, we recommend using VS Code and Node.js environment, or simply right-click in your browser > Inspect > Console.

Variables: Storing Data

In modern JavaScript (ES6+), we use let and const. Avoid the old var.

1. let (Changeable)

Use let when you expect the value to change later.

let score = 0;
score = 10; // Totally fine
console.log(score); // Output: 10

2. const (Constant)

Use const for values that should never be reassigned. This is the default choice for 90% of your code.

const pi = 3.14;
// pi = 3.15; // Error! Assignment to constant variable.

Data Types

JavaScript has a few basic types:

1. String: Text. "Hello World" or 'JavaScipt'.
2. Number: Integers and decimals. 42, 3.14.
3. Boolean: True or False. true, false.
4. Null: Intentionally empty. null.
5. Undefined: Variable declared but not assigned. undefined.

const name = "Jack";     // String
let age = 30;            // Number
let isStudent = false;   // Boolean
let emptyValue = null;   // Null
let notAssigned;         // Undefined

Template Literals

The modern way to combine strings and variables using backticks (`).

const name = "Alice";
const greeting = `Hello, ${name}! Welcome to the course.`;
console.log(greeting); 
// Output: Hello, Alice! Welcome to the course.

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Homework for Day 1:

1. Open your browser console (F12).
2. Create a constant for your birth year.
3. Create a variable for the current year.
4. Calculate your age and log it using a template literal: "I am X years old".

See you in Day 2 for Control Flow!