const heading = document.getElementById("main-title");

💡The DOM isn’t part of JavaScript — it's provided by the browser! JavaScript just gives us the tools to work with it. 🤯

'use strict';


function testStrict() {
let x = 10;
console.log(x);
}

Show alerts and messages
Handle button clicks
Create games
Validate forms (like checking if a name was entered)
Change content on the page without reloading

🧪Example:
alert("Hello, world!"); // Try this one on your console.

String – Text
👉 "Hello"
Number – Numbers
👉 42, 3.14
Boolean – True or false
👉 true, false
Undefined – A variable that hasn’t been given a value yet
👉 let x;
Null – Intentionally empty
👉 let y = null;

Object – A collection of key-value pairs
👉 { name: "John", age: 25 }
Array – A list of values
👉 [1, 2, 3, 4]
Function – Reusable blocks of code
👉 function greet() { console.log("Hi!") }

Checking Data Types
To check the data type of a certain variable, we use the typeof operator.

// commenting the code itself with a single comment
// let firstName = 'Yared'; single line comment
// let lastName = 'M'; single line comment

/*
  let location = 'AddisAbaba';
  let age = 200;
  let isMarried = false;
  This is a Multiple line comment
*/

let – when the value can change

const – when the value won’t change

✅ Rules for Naming Variables

To create valid variable names, follow these rules:

No starting with numbers

❌ 1name → ❌
✅ name1 → ✅

Only letters, digits, $, and _ are allowed

❌ my-name → ❌
✅ my_name or myName → ✅

Use camelCase (recommended)

✅ userName, totalAmount

No spaces

❌ user name → ❌
✅ userName → ✅