Variables and Data Types

let and const

• let – reassignable.
• const – cannot be reassigned (object/array contents can still change).

javascript
let count = 0;
count = 1;

const name = \"Froquiz\";
// name = \"Other\";  // error

Prefer const by default; use let when you need to reassign.

Primitives

• number – integers and decimals.
• string – text (double or single quotes).
• boolean – true / false.
• undefined – uninitialized.
• null – intentional absence of value.

javascript
const age = 25;
const greeting = \"Hello\";
const active = true;

typeof

javascript
typeof 42        // \"number\"
typeof \"hello\"  // \"string\"
typeof true      // \"boolean\"

Strings

Template literals (backticks) for interpolation:

javascript
const msg = `User ${name} is ${age} years old`;