पैरामीटर डेकोरेटर और मेटाडेटा

@sealed
class BugReport {
  type = 'report';
  title: string;
  constructor(t: string) { this.title = t; }
}

function sealed(constructor: Function) {
  Object.seal(constructor);
  Object.seal(constructor.prototype);
}

function log(target: any, key: string, desc: PropertyDescriptor) {
  const orig = desc.value;
  desc.value = function(...args: any[]) {
    console.log('Calling', key);
    return orig.apply(this, args);
  };
}

function readonly(target: any, key: string) {
  Object.defineProperty(target, key, { writable: false });
}

function required(target: any, key: string, index: number) {
  const meta = Reflect.getMetadata('required', target, key) || [];
  meta.push(index);
  Reflect.defineMetadata('required', meta, target, key);
}

function role(name: string) {
  return function(target: any, key: string) {
    Reflect.defineMetadata('role', name, target, key);
  };
}

class UserController {
  @role('admin')
  deleteUser() {}
}

@Controller('users')
class UsersController {
  constructor(private usersService: UsersService) {}

  @Get()
  findAll(): User[] {
    return this.usersService.findAll();
  }
}

import 'reflect-metadata';
// Enable in tsconfig: experimentalDecorators: true, emitDecoratorMetadata: true

@first
@second
class Example {}
// Applied: second first, then first