Class: NexoEmitter<Events>

Defined in: src/events/NexoEmitter.ts:34

A minimal, synchronous event emitter for proxy-related instrumentation.

Remarks

NexoEmitter is a purpose-built event manager designed for performance-critical environments such as JavaScript Proxy traps. It executes listeners synchronously and supports event cancellation (defaultPrevented) and return value capture (returnValue).

This emitter intentionally does not support async listener chaining, and errors thrown by listeners will crash the app unless an 'error' handler is attached.

Usage Notes

• Use on(event, fn) to attach listeners.
• Use off(event, fn) to remove them.
• Use emit(event, data) to dispatch a NexoEvent or Error.

Behavior

• If an Error is passed to emit() (and the event is not "error"), it is re-emitted on "error".
• If no "error" listener exists, the app will throw to ensure fail-fast behavior.
• If a NexoEvent is emitted and defaultPrevented is false, listeners' returnValue will be ignored.

Example

const emitter = new NexoEmitter();
emitter.on("proxy.set", (event) => {
  if (event.key === "password") event.preventDefault();
});

emitter.emit("proxy.set", new NexoEvent({ key: "password" }));

Extended by

• Nexo
• ProxyWrapper

Type Parameters

• Events extends NexoEmitterEvents = NexoEmitterEvents

Implements

• NexoEmitter

Constructors

new NexoEmitter()

new NexoEmitter<Events>(): NexoEmitter<Events>

Returns

NexoEmitter<Events>

Methods

emit()

emit<K>(eventName, data): boolean

Defined in: src/events/NexoEmitter.ts:117

Emits an event and synchronously triggers all associated listeners.

Type Parameters

• K extends string

Parameters

eventName

K

The name of the event to emit.

data

Events[K] extends NexoEvent ? any[any] : Error

A NexoEvent or an Error.

Returns

boolean

true if any listeners were triggered; false otherwise.

Remarks

Listeners are executed immediately. If a listener throws, the error is re-emitted via the 'error' event.

If data is an Error and the event name is not 'error', it will be forwarded to the 'error' listeners.

Implementation of

nx.NexoEmitter.emit

---

off()

off<K>(event, listener): this

Defined in: src/events/NexoEmitter.ts:92

Unregisters a listener from the specified event.

Type Parameters

• K extends string

Parameters

event

K

The event name to stop listening to.

listener

FunctionLike<[Events[K]], Events[K] extends NexoEvent ? any[any]["returnValue"] : void>

The function to remove from the event's listener list.

Returns

this

The current instance for chaining.

Remarks

If the listener is not registered for the given event, this method does nothing. Only the exact function reference passed to on() can be removed.

Removing a listener helps avoid memory leaks and unnecessary processing.

Example

const handler = (event) => console.log('Accessed:', event.key);
emitter.on('proxy.get', handler);
emitter.off('proxy.get', handler);

Implementation of

nx.NexoEmitter.off

---

on()

on<K>(event, listener): this

Defined in: src/events/NexoEmitter.ts:60

Registers a listener for the specified event.

Type Parameters

• K extends string

Parameters

event

K

The event name to listen for.

listener

FunctionLike<[Events[K]], Events[K] extends NexoEvent ? any[any]["returnValue"] : void>

The function to call when the event is emitted.

Returns

this

The current instance for chaining.

Remarks

The listener will be called every time the event is emitted. Multiple listeners can be registered for the same event, and they will be executed in the order in which they were added.

This method does not check for duplicates — adding the same function multiple times will result in multiple calls.

Example

emitter.on('proxy.set', (event) => {
  console.log('Property set:', event.key);
});

Implementation of

nx.NexoEmitter.on