Your First Steps with JavaScript

Think about a website where you clicked a button and something immediately changed — a menu appeared, a score went up, or an image swapped. That instant reaction did not happen by accident. Someone wrote instructions to make the page respond to you. Those instructions are called JavaScript. Before you read on, try to answer this: what do you think is the difference between a web page that just displays information and one that reacts when you interact with it? Hold that thought — you are about to find out.

Every webpage is built from three layers that work together. HTML provides the structure — the headings, paragraphs, and images. CSS controls the style — colours, fonts, and layout. JavaScript is the third layer: it adds behaviour, making pages respond to what users do. JavaScript is a programming language that runs directly inside your web browser. When you visit a webpage, the browser reads the HTML and CSS first, then executes any JavaScript it finds. Because it runs in the browser, you can see results instantly without sending anything to a server. **Variables** are one of the most fundamental ideas in JavaScript. A variable is a named container that stores a value so your program can use it later. You create a variable with the keyword `let`, followed by a name you choose, then an equals sign, and then the value. let age = 13; let greeting = "Hello, world!"; The first line stores the number 13 in a variable called `age`. The second stores the text `Hello, world!` in a variable called `greeting`. Text values must be wrapped in quotation marks; numbers must not. **console.log()** is a built-in JavaScript command that prints a value to the browser's developer console — a hidden panel developers use to test and debug code. You pass the value or variable name inside the round brackets. console.log(greeting); // prints: Hello, world! console.log(age); // prints: 13 console.log(5 + 3); // prints: 8 The double forward-slash `//` marks a comment — a note for the human reader that JavaScript completely ignores. JavaScript can also react to events. An event is something the user does, such as clicking a button or moving the mouse. You can attach a piece of code called a function to an event so that code runs the moment the event happens. This is the mechanism behind every interactive button, form, and animation on the web.