version: "1.0.1" name: devtools-event-client description: Create typed EventClient for a library. Define event maps with typed payloads, pluginId auto-prepend namespacing, emit()/on()/onAll()/onAllPluginEvents() API. Connection lifecycle (5 retries, 300ms), event queuing, enabled/disabled state, SSR fallbacks, singleton pattern. Unique pluginId requirement to avoid event collisions. type: core library: '@tanstack/devtools-event-client' library_version: '0.10.12' sources:

• packages/event-bus-client/src/plugin.ts
• docs/event-system.md
• docs/building-custom-plugins.md

devtools-event-client

Typed event emitter/listener that connects application code to TanStack Devtools panels. Framework-agnostic. Works in React, Vue, Solid, Preact, and vanilla JS.

Setup

Install the package:

npm i @tanstack/devtools-event-client

The package has two entry points — the root export (the real client in development, a no-op tree-shaken out of production), and the /production subpath (always the real client, for libraries that want devtools events in production):

import { EventClient } from '@tanstack/devtools-event-client'

Constructor Options

Core Patterns

1. Define an Event Map and Create a Singleton Client

Define a TypeScript type mapping event suffixes to payload types. Extend EventClient and export a single instance at module level.

import { EventClient } from '@tanstack/devtools-event-client'
type StoreEvents = {
  'state-changed': { storeName: string; state: unknown; timestamp: number }
  'action-dispatched': { storeName: string; action: string; payload: unknown }
  reset: void
}
class StoreInspectorClient extends EventClient<StoreEvents> {
  constructor() {
    super({ pluginId: 'store-inspector' })
  }
}
// Module-level singleton -- one instance per plugin
export const storeInspector = new StoreInspectorClient()

Event map keys are suffixes only. The pluginId is prepended automatically. With pluginId: 'store-inspector' and key 'state-changed', the fully qualified event on the bus is 'store-inspector:state-changed'.

2. Emit Events

Call emit(suffix, payload) from library code. Pass only the suffix.

function dispatch(action: string, payload: unknown) {
  state = reducer(state, action, payload)
  storeInspector.emit('state-changed', {
    storeName: 'main',
    state,
    timestamp: Date.now(),
  })
  storeInspector.emit('action-dispatched', {
    storeName: 'main',
    action,
    payload,
  })
}

If the bus is not connected yet, events are queued in memory and flushed once the connection succeeds. If the connection fails after 5 retries (1.5s at default settings), the client gives up and subsequent emit() calls are silently dropped.

Connection to the bus is initiated lazily on the first emit() call, not on construction or on().

3. Listen to Events

All listener methods return a cleanup function.

`on(suffix, callback)` -- listen to a specific event from this plugin:

const cleanup = storeInspector.on('state-changed', (event) => {
  // event.type    === 'store-inspector:state-changed'
  // event.payload === { storeName: string; state: unknown; timestamp: number }
  // event.pluginId === 'store-inspector'
  console.log(event.payload.state)
})
// Stop listening
cleanup()

`on(suffix, callback, { withEventTarget: true })` -- also register on an internal EventTarget so events emitted and listened to on the same client instance are delivered immediately without going through the global bus:

const cleanup = storeInspector.on(
  'state-changed',
  (event) => {
    console.log(event.payload.state)
  },
  { withEventTarget: true },
)

`onAll(callback)` -- listen to all events from all plugins:

const cleanup = storeInspector.onAll((event) => {
  console.log(event.type, event.payload)
})

`onAllPluginEvents(callback)` -- listen to all events from this plugin only (filtered by pluginId):

const cleanup = storeInspector.onAllPluginEvents((event) => {
  // Only fires when event.pluginId === 'store-inspector'
  console.log(event.type, event.payload)
})

4. Connection Lifecycle and Disabling

The connection lifecycle is:

1. First emit() dispatches tanstack-connect and starts a retry loop.
2. Retries every reconnectEveryMs (default 300ms), up to 5 attempts.
3. On tanstack-connect-success, queued events are flushed in order.
4. After 5 failed retries, failedToConnect is set permanently. All subsequent emit() calls are silently dropped (not queued).

To disable the client entirely (e.g., in production):

class StoreInspectorClient extends EventClient<StoreEvents> {
  constructor() {
    super({
      pluginId: 'store-inspector',
      enabled: process.env.NODE_ENV !== 'production',
    })
  }
}

When enabled is false, emit() is a no-op and on()/onAll()/onAllPluginEvents() return no-op cleanup functions.

Common Mistakes

1. Including pluginId prefix in event names (CRITICAL)

EventClient auto-prepends the pluginId to all event names. Including the prefix manually produces a double-prefixed event name that nothing will match.

Wrong:

storeInspector.emit('store-inspector:state-changed', data)
// Dispatches 'store-inspector:store-inspector:state-changed'

Correct:

storeInspector.emit('state-changed', data)
// Dispatches 'store-inspector:state-changed'

This applies to on() as well. Pass only the suffix.

2. Creating multiple EventClient instances per plugin (CRITICAL)

Each EventClient instance manages its own connection, event queue, and listeners independently. Creating multiple instances for the same plugin causes duplicate handlers, multiple connection attempts, and unpredictable event delivery.

Wrong:

function MyComponent() {
  // New instance on every render
  const client = new StoreInspectorClient()
  client.emit('state-changed', data)
}

Correct:

// store-inspector-client.ts
export const storeInspector = new StoreInspectorClient()
// MyComponent.tsx
import { storeInspector } from './store-inspector-client'
function MyComponent() {
  storeInspector.emit('state-changed', data)
}

3. Non-unique pluginId causing event collisions (CRITICAL)

Two plugins with the same pluginId share an event namespace. Events emitted by one are received by listeners on the other. Choose a unique, descriptive pluginId (e.g., 'my-org-store-inspector' rather than 'store').

4. Not realizing events drop after 5 failed retries (HIGH)

After 5 retries (1.5s at default reconnectEveryMs: 300), failedToConnect is set permanently. Subsequent emit() calls are silently dropped -- they are not queued and will never be delivered, even if the bus becomes available later.

If you need events to survive longer startup delays, increase reconnectEveryMs:

super({ pluginId: 'store-inspector', reconnectEveryMs: 1000 })
// 5 retries * 1000ms = 5s window

There is no way to increase the retry count (hardcoded to 5).

5. Expecting connection on construction or on() (HIGH)

The connection to the event bus is initiated lazily on the first emit() call. Calling on() alone does not trigger a connection. If your panel calls on() but the library side never calls emit(), the client never connects to the bus.

This means if you only listen (no emitting), the on() handler still works for events dispatched directly on the global event target, but the connection handshake (tanstack-connect / tanstack-connect-success) never runs.

6. Using non-serializable payloads (HIGH)

When the server event bus is enabled, events are serialized via JSON for transport over WebSocket/SSE/BroadcastChannel. Payloads containing functions, DOM nodes, class instances, Map/Set, or circular references will fail silently or lose data.

Wrong:

storeInspector.emit('state-changed', {
  storeName: 'main',
  state,
  callback: () => {}, // Function -- not serializable
  element: document.body, // DOM node -- not serializable
})

Correct:

storeInspector.emit('state-changed', {
  storeName: 'main',
  state: JSON.parse(JSON.stringify(state)), // Ensure serializable
  timestamp: Date.now(),
})

7. Forgetting the root export no-ops in production (HIGH)

The root import of @tanstack/devtools-event-client resolves to a no-op when process.env.NODE_ENV !== 'development', and the real client is tree-shaken out of production bundles. This is the default and what you want for most libraries — your emit() calls cost nothing in production.

"Outside development" includes when NODE_ENV is unset — common in plain Node scripts, some SSR dev servers, and test runners — so the root import resolves to the no-op there too. Set NODE_ENV=development, or use the /production subpath, to get the real client in those contexts.

// dev: real client — production: no-op, removed from the bundle
import { EventClient } from '@tanstack/devtools-event-client'

If you are publishing an open-source library and deliberately want devtools events to keep working in production, import from the /production subpath, which always ships the real client:

import { EventClient } from '@tanstack/devtools-event-client/production'

The enabled constructor option still works for fine-grained runtime control, but you no longer need to guard emit() calls manually for bundle size — the root export handles that for you.

See Also

• devtools-instrumentation -- after creating a client, instrument library code with strategic emissions
• devtools-plugin-panel -- the client emits events, the panel listens using the same event map
• devtools-bidirectional -- two-way communication between panel and application using the same EventClient