Types and Operators

Every value in JavaScript has a type. Six cover most beginner code.

The primitives

const name = "Ada"; // string — text in quotes
const year = 2026; // number — integers and decimals alike
const pi = 3.14159; // also a number
const isLive = true; // boolean — true or false
let nothing = null; // null — deliberately "no value"
let notSet; // undefined — declared, never assigned

null and undefined both mean "nothing here" — the difference is who did it: null is a deliberate choice by the programmer; undefined means the value was never set.

Numbers and arithmetic

const price = 19.99;
const quantity = 3;

price * quantity; // 59.97  (multiplication)
10 + 3; // 13
10 / 4; // 2.5
10 % 3; // 1   remainder — "% is the remainder operator"

% (remainder) is surprisingly useful: n % 2 === 0 tests whether a number is even.

Strings: joining and building

const first = "Ada";
const last = "Lovelace";

first +
  " " +
  last // "Ada Lovelace" — + joins strings
  `Full name: ${first} ${last}`; // template literal (backticks)
first.length; // 3 — strings have properties too
name.toUpperCase(); // "ADA" — and methods

Comparisons → booleans

const age = 20;

age >= 18; // true
age === 20; // true  — strict equality (three equals: always use this)
age !== 21; // true  — strict inequality

Always use === and !==. The loose versions (==) do surprising type conversions — a classic bug source you will simply never need.

Logic: &&, ||, !

const age = 20;
const hasTicket = true;

age >= 18 && hasTicket; // true — AND: both sides must be true
age < 12 || age > 65; // false — OR: at least one side true
!hasTicket; // false — NOT: flips the boolean

What you learned

• Six primitives; null (deliberate) vs undefined (not yet set)
• Arithmetic including the remainder %
• Template literals build strings; ===/!== for comparisons
• &&, ||, ! combine booleans

Next: programs that decide and repeat.