Funktionen mit Typen

function addiere(a: number, b: number): number {
  return a + b;
}
const mal = (a: number, b: number): number => a * b;

console.log(addiere(2, 3), mal(4, 5));

function gruss(name: string, anrede?: string): string {
  return `${anrede ?? "Hallo"} ${name}`;
}
function potenz(basis: number, exponent: number = 2): number {
  return basis ** exponent;
}
console.log(gruss("Mia"), "|", gruss("Tom", "Moin"));
console.log(potenz(5), potenz(2, 10));

function summe(...zahlen: number[]): number {
  return zahlen.reduce((s, z) => s + z, 0);
}
console.log(summe(1, 2, 3), summe());

function logge(text: string): void {
  console.log("LOG:", text);
}
function fehler(nachricht: string): never {
  throw new Error(nachricht);
}
logge("fertig");
try { fehler("kaputt"); } catch (e) { console.log((e as Error).message); }

type Rechner = (a: number, b: number) => number;

const plus: Rechner = (a, b) => a + b;        // Parametertypen werden abgeleitet
const minus: Rechner = (a, b) => a - b;

function anwenden(f: Rechner, x: number, y: number): number {
  return f(x, y);
}
console.log(anwenden(plus, 7, 3), anwenden(minus, 7, 3));
console.log([1, 2, 3].map((n) => n * 2));      // n wird als number erkannt

function laenge(x: string): number;
function laenge(x: unknown[]): number;
function laenge(x: string | unknown[]): number {
  return x.length;
}
console.log(laenge("Hallo"), laenge([1, 2]));

function zeige({ name, alter = 18 }: { name: string; alter?: number }): string {
  return `${name} (${alter})`;
}
console.log(zeige({ name: "Mia" }), zeige({ name: "Tom", alter: 30 }));

interface Zaehler { stand: number; erhoehe(this: Zaehler): void }
const z: Zaehler = { stand: 0, erhoehe() { this.stand++; } };
z.erhoehe();
console.log(z.stand);

async function lade(id: number): Promise<{ id: number; name: string }> {
  await new Promise((r) => setTimeout(r, 10));
  return { id, name: "Nutzer " + id };
}
lade(7).then((n) => console.log(n.name));

function addiere(a: number, b: number): number { return a + b; }
addiere(1);