decorator-example.ts

export const Badthing = (): MethodDecorator => {
  return (
    target: Object,
    key: string | symbol,
    descriptor: PropertyDescriptor,
  ) => {
    const originalMethod = descriptor.value;
    console.log("Badthing");
    descriptor.value = (...args: any[]) => {
      args[0] = 'I do not ' + args[0];
      return originalMethod.apply(this, args);
    };

    return descriptor;
  };
};

class SomethingNice {
  @Badthing()
  public doGoodThings(task?: string) {
    console.log(task);
  }
}

const x = new SomethingNice();
x.doGoodThings("Wash dishes");