Rest-Parameter und Spread mit Typen

Willkommen

Rest-Parameter typisieren

function sum(...nums: number[]): number {
  return nums.reduce((a, b) => a + b, 0);
}
console.log(sum(1, 2, 3, 4)); // 10

Rest-Parameter nach erforderlichen Parametern

function log(level: string, ...messages: string[]): void {
  console.log(level, messages.join(' '));
}
log('INFO', 'Server', 'started', 'on', 'port', '3000');

Arrays in Funktionen spreizen

function add(a: number, b: number): number { return a + b; }
const args: [number, number] = [1, 2];
add(...args); // OK — tuple spread is type-safe

Spreizen regulärer Arrays

const nums = [1, 2]; // number[] — length unknown
// add(...nums); // Error: spread must match parameters
const pair: [number, number] = [1, 2];
add(...pair); // OK — tuple has known length

Rest-Parameter und arguments-Objekt

Objekte spreizen (keine Rest-Parameter)

const a = { x: 1, y: 2 };
const b = { z: 3 };
const c = { ...a, ...b }; // { x: number; y: number; z: number }

Eigenschaften mit Spread überschreiben

const base = { color: 'red', size: 5 };
const updated = { ...base, color: 'blue' };
// { color: 'blue', size: 5 }

Typisierter Spread in Arrays

const a: number[] = [1, 2];
const b: number[] = [3, 4];
const c: number[] = [...a, ...b]; // [1, 2, 3, 4]

Variadischer Tupel-Rest

type Strings = string[];
type StringsAndNumber = [...Strings, number];
const t: StringsAndNumber = ['a', 'b', 42];

Rest beim Destrukturieren

const [first, ...rest]: number[] = [1, 2, 3, 4];
// first: number, rest: number[]

Kurzer Test

Zusammenfassung