Authoring ComfyUI v2 frontend extensions

ComfyUI v2 Frontend Extension API

The v2 extension API is the published npm package @comfyorg/extension-api. It replaces the legacy app.registerExtension() / nodeType.prototype monkey-patching model with a typed, tree-shakeable, import-based API.

If you are converting an existing v1 extension, read references/migrate-v1-to-v2.md for a pattern-by-pattern mapping.

Mental model

v1 (legacy)	v2 (@comfyorg/extension-api)
One giant app.registerExtension({...}) call	One defineX per concern, each independently disposable
window.app / app.* globals	Direct import from the package; no window.app at module-eval time
nodeType.prototype.onExecuted = ... patching	node.on('executed', fn) on a NodeHandle
Mutate widget.value, assign widget.callback	widget.setValue(v) / widget.on('valueChange', fn)
api.addEventListener('execution_start', fn)	execution.on('start', fn) (typed namespaces)
Manual removeEventListener bookkeeping	Every subscription returns Unsubscribe; every defineX returns DisposableHandle

Core principles baked into the API:

• Import, don't reach for globals. import { defineNode } from '@comfyorg/extension-api'. No window.app dependency at module evaluation time.
• Read via getters, write via command-dispatch setters. getValue() reads; setValue() dispatches an undo-able, serializable command. Read-only invariants (set at construction) are readonly accessors (node.type, widget.name).
• Observe via typed on(...) subscriptions. Each returns an Unsubscribe cleanup function. No Vue refs/signals are ever exposed; Vue reactivity is the internal engine only.
• Everything is disposable. Every defineX returns a DisposableHandle with an idempotent, synchronous dispose().

Registration entry points

All imported from @comfyorg/extension-api:

Function	Purpose	Returns
defineNode(opts)	Primary entry — react to node lifecycle (replaces prototype patching)	NodeExtensionOptions
defineExtension(opts)	App-scoped lifecycle (init/setup) + shell UI host	ExtensionOptions
defineWidget(opts)	Register a custom widget type (DOM via mount)	WidgetExtensionOptions
defineSidebarTab(opts)	Add a left-sidebar tab (Vue or custom)	DisposableHandle
defineBottomPanelTab(opts)	Add a bottom-panel tab	DisposableHandle
defineToolbarButton(opts)	Add an action-bar button	DisposableHandle
defineCommand(opts)	Register an invokable command	DisposableHandle
defineHotkey(opts)	Bind a key combo to a command id	DisposableHandle
defineSetting(opts)	Add a settings-menu entry	DisposableHandle
defineAboutBadge(opts)	Add a badge to the About page	DisposableHandle

Imperative carve-outs (fire-and-forget, not defineX, no handle): toast, notify.

A single extension file typically exports a default defineExtension/defineNode result and calls the shell-UI defineX functions inside setup() or at module scope. They queue safely before the app boots.

defineNode — the primary entry point

Reacts to node lifecycle. nodeCreated fires once per node instance (typed in, pasted, duplicated, or loaded without an existing workflow). loadedGraphNode fires once when a node is restored from a saved workflow (widget values already populated). Exactly one of them fires per node entity, never both.

import { defineNode, onNodeMounted, onNodeRemoved } from '@comfyorg/extension-api'

export default defineNode({
  name: 'my-org.executed-logger',
  // Filter to specific comfyClass names. Omit to receive every node type.
  nodeTypes: ['KSampler', 'KSamplerAdvanced'],

  // MUST be synchronous. Runs inside a Vue EffectScope; everything registered
  // here (subscriptions, onNodeMounted) auto-disposes when the node is removed.
  nodeCreated(node) {
    // Read-only invariants
    console.log(node.type, node.comfyClass, node.id)

    // Subscribe to backend execution completion (replaces onExecuted patching)
    node.on('executed', (e) => {
      console.log('output:', e.output) // Record<string, unknown>
    })

    // Lifecycle hooks — call SYNCHRONOUSLY (never after an await)
    onNodeMounted(() => {
      // Node fully mounted; DOM/canvas ready.
    })
    onNodeRemoved(() => {
      // Cleanup: abort fetches, close sockets. Does NOT fire on subgraph promotion.
    })
  },

  loadedGraphNode(node) {
    // Node restored from a saved workflow; widget values are already set.
  }
})

NodeHandle surface (Phase A)

Member	Kind	Notes
id: string	readonly	Opaque token. Compare with node.equals(other), never by slicing.
equals(other)	method	Canonical identity comparison.
type: string	readonly	LiteGraph node type.
comfyClass: string	readonly	Backend class name.
getProperty<T>(key) / getProperties() / setProperty(key, v)	methods	Per-instance props (migration shim — prefer widget values).
getInputs() / getOutputs()	methods	ReadonlyArray<Readonly<SlotInfo>> — frozen views.
on('executed', fn)	method	Execution complete → NodeExecutedEvent { output }.
on('removed', fn)	method	Node deleted (not subgraph promotion).
on('configured', fn)	method	Loaded from saved workflow (after widget values restored).
on('beforeSerialize', fn)	method	Deprecated — use widget-level beforeSerialize (ADR-0010).

Position/size/title/mode getters and slot/connection events are deferred in Phase A. Do not rely on getPosition, setSize, getMode, on('connected').

Nodes cannot enumerate or reference their widgets (node.getWidget(name) was removed). Use defineWidget and the mount context's ctx.widget handle.

defineExtension — app lifecycle + shell UI

Use for app-wide setup and to host shell-UI registrations. setup() runs at the early registration point; use the imported onMounted hook for work that needs the app fully initialized.

import {
  defineExtension,
  onMounted,
  onUnmounted,
  execution,
  toast
} from '@comfyorg/extension-api'

export default defineExtension({
  name: 'my-org.my-extension',
  setup() {
    // Register late-lifecycle work via onMounted (called synchronously here).
    onMounted(() => {
      const off = execution.on('start', () => {
        toast.show({ severity: 'info', summary: 'Run started' })
      })
      onUnmounted(off) // tidy teardown
    })
  }
})

A note on the setup() signature. The source-of-truth API uses implicit-context hooks: import onMounted/onNodeMounted/etc. and call them synchronously inside setup() (mirrors Vue's Composition API). An early package draft showed a setup(ctx) { ctx.onNodeMounted(...) } context-argument style; prefer the imported-hook form above, which is what the current API exports.

Context-scoped lifecycle hooks are imported and called synchronously inside defineExtension's setup(): onBeforeMount, onMounted, onUnmounted, onActivated, onDeactivated. defineSidebarTab/defineBottomPanelTab take no setup field; adding one is a type error. onActivated/onDeactivated fire when the surrounding tab or panel is shown or hidden.

defineWidget — custom widget types with DOM

Widgets are declared in the Python node's INPUT_TYPES, never created at runtime (node.addWidget is forbidden). defineWidget registers a type and the DOM mount hook the runtime invokes against a host <div> it owns. mount is optional; omit it for value-only widgets that render through the native renderer.

import { defineWidget, type WidgetCleanup } from '@comfyorg/extension-api'

export default defineWidget({
  name: 'my-org.color-picker',
  type: 'COLOR_PICKER', // referenced from Python INPUT_TYPES

  // The SOLE DOM seam. Capture host + constructed DOM via closure — there is
  // no widget.element accessor.
  mount(host, ctx): WidgetCleanup {
    const input = document.createElement('input')
    input.type = 'color'
    input.value = String(ctx.widget.getValue() ?? '#000000')
    input.addEventListener('input', () => ctx.widget.setValue(input.value))
    host.appendChild(input)

    // ctx.widget / ctx.node are the only legal handles here.
    ctx.widget.on('valueChange', (e) => {
      input.value = String(e.newValue ?? '#000000')
    })

    // Optional cleanup — fires once on widget destruction (NOT on host remount).
    return () => input.remove()
  }
})

WidgetMountContext also exposes onUnmount(fn), onBeforeRemount(fn), and onAfterRemount(fn => ...) for host-move scenarios (graph↔app mode, subgraph promotion). The mount body is not re-invoked across a remount; only the remount hooks fire.

WidgetHandle surface

Member	Kind	Notes
id / equals(other)	readonly / method	Opaque identity.
name / widgetType / label	readonly	Set from INPUT_TYPES schema.
getValue<T>() / setValue(v)	methods	setValue dispatches an undo-able command.
options	readonly	Readonly<WidgetOptions> snapshot. Writes raise TS errors.
getOption<K>(key) / setOption(key, v)	methods	Per-instance overrides (e.g. min/max/step).
setHeight(px)	method	Resize the reserved host height (DOM widgets).
on('valueChange', fn)	method	WidgetValueChangeEvent { oldValue, newValue }.
on('optionChange', fn)	method	WidgetOptionChangeEvent { key, oldValue, newValue }.
on('beforeSerialize', fn)	method	Only async-allowed event. e.value + e.setSerializedValue(v).
on('beforeQueue', fn)	method	Pre-queue validation. Call e.reject(msg) to cancel.

// Serialization override (the SOLE serialization interface in v2):
widget.on('beforeSerialize', (e) => {
  e.setSerializedValue(processDynamicPrompt(widget.getValue()))
})

// Async serialization (e.g. capture a webcam frame before queueing):
widget.on('beforeSerialize', async (e) => {
  e.setSerializedValue(await captureFrame())
})

// Pre-queue validation (replaces app.queuePrompt monkey-patching):
widget.on('beforeQueue', (e) => {
  if (!widget.getValue()) e.reject('Prompt text is required before queueing.')
})

Typed event namespaces

Four module-level singletons replace api.addEventListener('...'). Each on() returns an Unsubscribe. Subscriptions made inside a setup() body auto-dispose on unmount; subscriptions made elsewhere are the caller's responsibility.

Namespace	Events (canonical)	Wire mapping
execution	start, end, error, interrupted, cached, executing, progress, preview	execution_<evt>
graph	changed, …	graph:<evt>
server	status, logs, reconnected, feature_flags, assets, + custom-node events	raw event name
workbench	notification, …	workbench:<evt>

import { execution, server } from '@comfyorg/extension-api'

const off = execution.on('progress', (e) => console.log('progress', e))
// Custom-node events ride the `server` namespace with arbitrary names:
server.on('my-org.my-node.update', (e) => console.log(e))
// later:
off()

Payloads default to unknown today. Narrow them with TS module augmentation:

declare module '@comfyorg/extension-api' {
  interface ExecutionEventPayloads {
    start: { promptId: string }
    progress: { value: number; max: number }
  }
  interface ServerEventPayloads {
    'my-org.my-node.update': { nodeId: string; text: string }
  }
}

The augmentable interfaces are GraphEventPayloads, ExecutionEventPayloads, ServerEventPayloads, and WorkbenchEventPayloads.

Shell UI registrations

Each returns a DisposableHandle. Safe to call at module scope (they queue until the app boots) or inside setup().

import {
  defineCommand,
  defineHotkey,
  defineToolbarButton,
  defineSetting,
  defineAboutBadge
} from '@comfyorg/extension-api'

// Command — id, function, optional label/icon/tooltip.
const cmd = defineCommand({
  id: 'my-org.do-the-thing',
  label: 'Do The Thing',
  function: () => { /* ... */ }
})

// Hotkey — binds a key combo to an already-registered command id.
// `mod` = cmd on macOS, ctrl elsewhere.
defineHotkey({ keys: 'mod+shift+k', commandId: 'my-org.do-the-thing' })

// Action-bar button — id (for dispose), icon, onClick.
defineToolbarButton({
  id: 'my-org.help',
  icon: 'pi-question-circle',
  tooltip: 'Get help',
  onClick: () => openHelp()
})

// Setting — widen the id when not augmenting the Settings keymap.
defineSetting({
  id: 'my-org.enabled' as never,
  name: 'Enable my extension',
  type: 'boolean',
  defaultValue: false
})

// About-page badge.
defineAboutBadge({
  label: 'GitHub',
  url: 'https://github.com/me/my-ext',
  icon: 'pi-github'
})

// Tear down any registration:
cmd.dispose() // idempotent + synchronous

CommandDefinition fields: id (required), function: (metadata?) => void | Promise<void> (required), optional label / icon / tooltip (each string | (() => string)), menubarLabel, versionAdded.

defineSidebarTab — embedded panels (e.g. a chat panel)

A sidebar tab hosts a rich embedded UI such as a chat panel. It comes in two flavors: type: 'vue' (mount a Vue component) or type: 'custom' (imperative render(container) / destroy()). Both share the base fields id, title, optional icon, iconBadge, tooltip, label.

Vue component tab

import { defineSidebarTab } from '@comfyorg/extension-api'
import ChatPanel from './ChatPanel.vue'

const chatTab = defineSidebarTab({
  id: 'my-org.chat',
  title: 'Chat',
  type: 'vue',
  icon: 'pi-comments',
  component: ChatPanel
})
// chatTab.dispose() removes the tab.

Custom (framework-free) chat panel

When you don't want a Vue dependency, use type: 'custom' and build the DOM yourself. render receives the container; destroy is your teardown.

import {
  defineExtension,
  defineSidebarTab,
  execution,
  server,
  type Unsubscribe
} from '@comfyorg/extension-api'

export default defineExtension({
  name: 'my-org.chat-panel',
  setup() {
    const subscriptions: Unsubscribe[] = []

    defineSidebarTab({
      id: 'my-org.chat',
      title: 'Chat',
      type: 'custom',
      icon: 'pi-comments',

      render(container: HTMLElement) {
        const log = document.createElement('div')
        log.className = 'chat-log'

        const form = document.createElement('form')
        const input = document.createElement('input')
        input.placeholder = 'Ask something…'
        const send = document.createElement('button')
        send.type = 'submit'
        send.textContent = 'Send'
        form.append(input, send)

        const append = (who: string, text: string) => {
          const line = document.createElement('p')
          line.textContent = `${who}: ${text}`
          log.appendChild(line)
          log.scrollTop = log.scrollHeight
        }

        form.addEventListener('submit', (ev) => {
          ev.preventDefault()
          const text = input.value.trim()
          if (!text) return
          append('You', text)
          input.value = ''
          // Forward to a backend node/server event, stream the reply, etc.
        })

        container.append(log, form)

        // Stream backend replies via the server namespace (custom-node event).
        subscriptions.push(
          server.on('my-org.chat.reply', (e) => append('Assistant', String(e)))
        )
        // React to runs to show status in the panel.
        subscriptions.push(
          execution.on('start', () => append('System', 'Run started…'))
        )
      },

      destroy() {
        for (const off of subscriptions) off()
        subscriptions.length = 0
      }
    })
  }
})

defineBottomPanelTab has the same vue / custom shapes (base fields id, optional title/titleKey, optional targetPanel: 'terminal' | 'shortcuts').

Toasts

toast and notify are inline imperative (no defineX, no handle). Call from any setup() body or hook closure.

import { toast } from '@comfyorg/extension-api'

toast.show({ severity: 'error', summary: 'Workflow failed', detail: err.message, life: 4000 })
toast.removeAll()

notify({ kind, message, detail, life }) is a deprecated 1:1 wrapper over toast.show. Prefer toast.show directly.

Node identity helpers

For referencing nodes across subgraph boundaries or execution runs, use the branded identity types rather than raw integer node IDs:

import {
  createNodeLocatorId, parseNodeLocatorId, isNodeLocatorId,
  createNodeExecutionId, parseNodeExecutionId, isNodeExecutionId,
  type NodeLocatorId, type NodeExecutionId
} from '@comfyorg/extension-api'

const locator: NodeLocatorId = createNodeLocatorId(subgraphUuid, localNodeId)
// NodeExecutionId encodes a node's path through nested subgraphs as an array of node ids
// (joined with ':'). Pass the array, not positional args:
const execId: NodeExecutionId = createNodeExecutionId([localNodeId])

if (isNodeLocatorId(maybe)) {
  // parseNodeLocatorId returns { subgraphUuid: string | null; localNodeId: NodeId }
  const { subgraphUuid, localNodeId } = parseNodeLocatorId(maybe)
}

NodeLocatorId arrives from workflow JSON; NodeExecutionId arrives from websocket frames. You receive these from event payloads, which is why they're public (unlike the internal *EntityId brands, which are not exported).

Disposal contract

Every defineX returns DisposableHandle { dispose(): void }:

• Idempotent. Calling dispose() again is a safe no-op.
• Synchronous. Teardown happens synchronously inside dispose().
• Independent. Disposing handle A does not affect B or C. Sequence calls explicitly when teardown order matters (e.g. drop a hotkey before its command).
• Pre-mount safe. Disposing before the app boots removes the spec from the pending queue so it never mounts.

const handles = [
  defineCommand({ id: 'my.cmd', function: () => {} }),
  defineHotkey({ keys: 'mod+k', commandId: 'my.cmd' }),
  defineSidebarTab({ id: 'my.tab', title: 'Tab', type: 'vue', component: MyTab })
]
// Full teardown:
for (const h of handles.reverse()) h.dispose()

Common mistakes

1. Calling lifecycle hooks after await. onNodeMounted / onMounted / onUnmounted rely on implicit scope context and must be called synchronously inside the setup()/nodeCreated body. After an await the scope is gone: it throws in dev and is a silent no-op in prod. Kick off async work in the body, but register hooks first.
2. Reaching for window.app or app.*. v2 has no window.app dependency at module-eval time. Import everything from @comfyorg/extension-api.
3. Patching nodeType.prototype. Replaced by defineNode + node.on(...). Prototype patching does not interoperate with the v2 handle model.
4. Mutating reads. node.getInputs(), widget.options, and Point/Size tuples are frozen/Readonly; assignment raises TS errors. Use the setter methods (widget.setOption, widget.setValue).
5. Assigning widget.value / widget.callback / widget.serializeValue. Use setValue(), on('valueChange'), and on('beforeSerialize'). serializeValue is read-only in v2.
6. Trying to disable widget serialization. There is no serialize: false and no skip() in v2. If a widget should not contribute to the payload, it should not be a widget. The only serialization interface is widget.on('beforeSerialize', fn) + e.setSerializedValue(v).
7. Creating widgets at runtime. node.addWidget(...) / node.addDOMWidget(...) are removed. Declare widgets in the Python INPUT_TYPES; render custom DOM via defineWidget({ mount }).
8. Enumerating widgets from a node. node.getWidget(name) / node.getWidgets() were removed (nodes cannot reference widgets). Use a defineWidget mount context's ctx.widget, or share state via the server event bus.
9. Using node-level beforeSerialize. Deprecated (ADR-0010). Store extension state in a widget and use widget-level beforeSerialize.
10. Forgetting to dispose. Long-lived subscriptions made outside a setup() context, and every defineX handle, leak unless you call the returned Unsubscribe / dispose(). Inside setup() they auto-dispose on unmount.
11. Relying on deferred Phase A exports. Position/size/title/mode getters and slot/connection events are not yet exported. Don't write code against them.

Sources

• Official: npm package @comfyorg/extension-api at https://www.npmjs.com/package/@comfyorg/extension-api
• Empirical: none; the API was transcribed from the published package, not reverse-engineered from a working graph.