Lesson 1 — Basic types

Labels for your values

TypeScript is JavaScript plus types: labels that say what kind of value a variable holds. You write them after a colon — name: string for text, count: number for numbers, done: boolean for true/false. The TypeScript checker reads these labels before the code runs and warns you about mistakes, like adding a word to a number.

const city: string = "Oslo";
let year: number = 2026;
// year = "soon";  ← error: string is not a number

Why it matters: types catch typos and wrong values while you write, instead of after your users find them.