EventEmitter<Events>
Minimal typed event emitter backing the puppeteer-style Page event API.
The optional onCountChange hook fires whenever an event's listener count
changes (adds, removes, once auto-removal, removeAllListeners). Page uses
it to lazily open a subscription on the 0→1 transition and close it on 1→0.
Listeners are stored in a Set, so registering the same function twice for
an event is deduped to a single registration (one emit call, one off to
remove) — unlike Node's EventEmitter, which keeps duplicates. This is
intentional: it keeps the 0→1/1→0 count transitions that drive lazy
subscriptions unambiguous. Wrap in distinct closures if you need duplicates.
Type Parameters
| Type Parameter |
|---|
Events |
Constructors
Constructor
new EventEmitter<Events>(onCountChange?): EventEmitter<Events>;
Parameters
| Parameter | Type |
|---|---|
onCountChange? | (event, count) => void |
Returns
EventEmitter<Events>
Methods
emit()
emit<K>(event, payload): boolean;
Invoke every listener for event. Returns whether any listener ran.
Type Parameters
| Type Parameter |
|---|
K extends string | number | symbol |
Parameters
| Parameter | Type |
|---|---|
event | K |
payload | Events[K] |
Returns
boolean
listenerCount()
listenerCount<K>(event): number;
Type Parameters
| Type Parameter |
|---|
K extends string | number | symbol |
Parameters
| Parameter | Type |
|---|---|
event | K |
Returns
number
off()
off<K>(event, listener): this;
Type Parameters
| Type Parameter |
|---|
K extends string | number | symbol |
Parameters
| Parameter | Type |
|---|---|
event | K |
listener | Listener<Events[K]> |
Returns
this
on()
on<K>(event, listener): this;
Type Parameters
| Type Parameter |
|---|
K extends string | number | symbol |
Parameters
| Parameter | Type |
|---|---|
event | K |
listener | Listener<Events[K]> |
Returns
this
once()
once<K>(event, listener): this;
Type Parameters
| Type Parameter |
|---|
K extends string | number | symbol |
Parameters
| Parameter | Type |
|---|---|
event | K |
listener | Listener<Events[K]> |
Returns
this
removeAllListeners()
removeAllListeners<K>(event?): this;
Type Parameters
| Type Parameter |
|---|
K extends string | number | symbol |
Parameters
| Parameter | Type |
|---|---|
event? | K |
Returns
this