TypeScript の MethodDecorator メモ

declare type MethodDecorator = <T>(target: Object, propertyKey: string | symbol, descriptor: TypedPropertyDescriptor<T>) => TypedPropertyDescriptor<T> | void;

export function Decorator(): MethodDecorator {
  return (
    target: any,
    methodName: string | symbol,
    descriptor: TypedPropertyDescriptor<any>,
  ) => {
    // デコレータを付与したメソッド
    const originalMethod = descriptor.value;

    console.log({ target, methodName, descriptor });
    descriptor.value = function (...args: any[]) {
      // 引数
      console.log({ args });
      const result = originalMethod.apply(this, args);
      return result;
    };
  };
}

    Reflect.getMetadataKeys(originalMethod).forEach(previousMetadataKey => {
      const previousMetadata = Reflect.getMetadata(previousMetadataKey, originalMethod)
      Reflect.defineMetadata(previousMetadataKey, previousMetadata, descriptor.value)
    })

    Object.defineProperty(descriptor.value, 'name', { value: originalMethod.name, writable: false })