Variables and Data Types

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`;