Introduction to JavaScript

JavaScript is a programming language used to add interactivity to web pages. It's one of the core technologies of the web, alongside HTML and CSS. Below are some key JavaScript concepts every beginner should learn.

🔍 typeof Operator

The typeof operator is used to determine the type of a value. For example, typeof undefined returns 'undefined'.

console.log(typeof undefined); // 'undefined'

🔒 Declaring Constants with const

const is used to declare variables that cannot be reassigned. It provides block scope and is useful for fixed values.

const pi = 3.14;
// pi = 3.14159; // ❌ This will cause an error

🔗 Accessing Elements with getElementById

document.getElementById() is used to access an HTML element by its ID. If no element is found, it returns null.

let element = document.getElementById('demo');
console.log(element); // null if no element with ID "demo"

🧩 Combining Strings with concat()

The concat() method joins two or more strings. It doesn't change the original strings.

let a = "Hello, ";
let b = "world!";
let result = a.concat(b); // "Hello, world!"

📝 Writing Comments

Comments are used to explain code and are ignored during execution. In JavaScript, single-line comments start with //.

// This is a comment
let x = 5; // This is also a comment