Quick Start: PostboyCallbackMessage

A minimal working example of a callback message that returns a typed response.

1. Define the message

Create a class that extends PostboyCallbackMessage<T>.

import { PostboyCallbackMessage } from '@artstesh/postboy';
import { User } from './models/user.model';

export class GetUserQuery extends PostboyCallbackMessage<User | null> {
static readonly ID = 'user.load';

constructor(public readonly userId: string) {
super();
}
}

2. Register a handler

Inside a service, register a command handler using regCmd.

import {AppPostboyService} from '@shared/services/app-postboy.service';
import {GetUserQuery} from './messages/queries/get-user.query';

export class UserService {
  constructor(private postboy: AppPostboyService) {
    this.postboy.exec(new ConnectMessage(GetUserQuery, new Subject<GetUserQuery>));
    this.postboy.sub(GetUserQuery).subscribe((msg) => {
      // Synchronous or asynchronous logic
      const user = this.cache.get(msg.userId);
      msg.finish(user ?? null);
    });
  }

  private cache = new Map<string, User>();
}

3. Fire the callback and consume the response

Any component or service can send the query and subscribe to the result.

import {Component} from '@angular/core';
import {AppPostboyService} from '@shared/services/app-postboy.service';
import {GetUserQuery} from './messages/queries/get-user.query';

@Component({ /* ... */})
export class UserProfileComponent {
  constructor(private postboy: AppPostboyService) {
  }

  loadUser(id: string): void {
    this.postboy.fireCallback(new GetUserQuery(id)).subscribe((user) => {
      if (user) {
        console.log('User loaded:', user.name);
      } else {
        console.log('User not found');
      }
    });
  }
}

Key points

PostboyCallbackMessage<T> guarantees a typed response.
The handler must call msg.finish(result) to send the result back.
The sender receives the result via the observable returned by fireCallback.

24 апреля 2026