Publishing & Subscribing

This page covers the basic publish/subscribe primitives in PubSub MFE: how to publish messages, subscribe to topics, and manage subscription lifetimes.

Publish

Use bus.publish(topic, payload, options?) to send a message through the bus. The bus will wrap the payload into a standard message envelope which includes metadata (id, ts, topic, payload, meta, ...).

// TypeScript
bus.publish('cart.item.add', { sku: 'ABC123', qty: 1 })

// Add optional meta
bus.publish('user.login', { userId: 'u-1' }, { meta: { source: 'auth' } })

Notes:

• Publishing is synchronous from the caller's perspective (message is enqueued and dispatched to local subscribers). Delivery to remote transports (cross-tab) may be asynchronous depending on configured transports.
• You can provide meta and schemaVersion in options to help with tracing and validation.

Subscribe

Subscribe with bus.subscribe(topicPattern, handler, opts?). Subscriptions return an unsubscribe function.

const unsubscribe = bus.subscribe('cart.item.+', (msg) => {
  console.log('Item event:', msg.topic, msg.payload)
})

// Remove when no longer needed
unsubscribe()

Options:

• signal?: AbortSignal — remove the subscription when the signal is aborted.
• replay?: number — replay last N messages on subscribe.
• sourceFilter?: object — Source filter — only receive messages from specific sources.

One-time & Scoped Subscriptions

For short-lived listeners you can either call the returned unsubscribe() or use an AbortSignal:

const controller = new AbortController()

bus.subscribe('orders.#', handler, { signal: controller.signal })

// later
controller.abort() // removes all subscriptions created with this signal

Delivery Guarantees

PubSub MFE is designed to be lightweight and predictable:

• Local subscribers are invoked asynchronously in publish order (subject to handler isolation).
• Cross-tab or transport-delivered subscribers may receive messages asynchronously.
• There are no built-in guaranteed retries; if you need retries, implement them in your handler or using an intermediate adapter.

Best Practices

• Keep payloads small and focused (IDs + minimal data). Use a shared storage (IndexedDB) for large blobs.
• Use domain-oriented topic naming: domain.entity.action (e.g., cart.item.add).
• Use AbortSignal for lifecycle-managed subscriptions in frameworks.

See also: Topic Patterns and Handler Isolation.