TypeScript isn't just "JavaScript with types." Used well, it transforms how you think about code.

Discriminated unions are magic

type Result<T> = 
  | { success: true; data: T }
  | { success: false; error: string };

function process(r: Result<User>) {
  if (r.success) {
    console.log(r.data); // TypeScript knows this is User
  } else {
    console.log(r.error); // TypeScript knows this is string
  }
}

satisfies keyword

New in TS 4.9, it's a game-changer for type inference:

const config = {
  apiUrl: "https://api.example.com",
  timeout: 5000,
} satisfies Config;
// config.apiUrl is inferred as the literal string, not just 'string'

as const for literals

const COLORS = ["red", "blue", "green"] as const;
type Color = typeof COLORS[number]; // "red" | "blue" | "green"

Template literal types

type EventName = `on${Capitalize<string>}`;
const valid: EventName = "onClick"; // ✓
const invalid: EventName = "click"; // ✗

My favorite utility types

• Partial<T> — all properties optional
• Required<T> — all properties required
• Pick<T, K> — select specific properties
• Omit<T, K> — exclude specific properties
• Record<K, V> — create object type

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TypeScript's type system is Turing-complete. Use that power wisely.