#$subscriber

#Import

typescript

1import { $subscriber } from "alepha/topic";

#Overview

Creates a subscriber primitive to listen for messages from a specific topic.

Provides a dedicated message subscriber that connects to a topic and processes messages with custom handler logic, enabling scalable pub/sub architectures where multiple subscribers can react to the same events independently.

Key Features

Seamless integration with any $topic primitive
Full type safety inherited from topic schema
Real-time message delivery when events are published
Error isolation between subscribers
Support for multiple independent subscribers per topic

Common Use Cases

Notification services and audit logging
Analytics and metrics collection
Data synchronization and real-time UI updates

#Options

Option	Type	Required	Description
`topic`	`TopicPrimitive<T>`	Yes	The topic primitive that this subscriber will listen to for messages
`handler`	`TopicHandler<T>`	Yes	Message handler function that processes individual messages from the topic

#Examples

 1class UserActivityService { 2  dateTime = $inject(DateTimeProvider); 3  4  userEvents = $topic({ 5    name: "user-activity", 6    schema: { 7      payload: z.object({ 8        userId: z.text(), 9        action: z.enum(["login", "logout", "purchase"]),10        timestamp: z.number()11      })12    }13  });14 15  activityLogger = $subscriber({16    topic: this.userEvents,17    handler: async (message) => {18      const { userId, action, timestamp } = message.payload;19      await this.auditLogger.log({20        userId,21        action,22        timestamp23      });24    }25  });26 27  async trackUserLogin(userId: string) {28    await this.userEvents.publish({29      userId,30      action: "login",31      timestamp: this.dateTime.nowMillis()32    });33  }34}