ConstructorParameters and InstanceType

ConstructorParameters and InstanceType: working example

Run this standalone example after compiling with TypeScript 5.4+ in strict mode, targeting ES2022. Expected result: The program prints Ada: 3; changing the constructor’s parameter types updates the factory’s checked arguments.

class Person {
  constructor(public name: string, public visits: number) {}
  describe() { return `${this.name}: ${this.visits}`; }
}
type Args = ConstructorParameters<typeof Person>;
type PersonObject = InstanceType<typeof Person>;
function createPerson(...args: Args): PersonObject {
  return new Person(...args);
}
console.log(createPerson("Ada", 3).describe());

1. Expected result: The program prints Ada: 3; changing the constructor’s parameter types updates the factory’s checked arguments.
2. typeof Person refers to the constructor value’s type.
3. The rest parameter receives the extracted tuple, preserving order and parameter types.