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event-emitter.ts
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event-emitter.ts
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export type EventListener<E> = (event: E) => void
export class EventEmitter<EventMap> {
private readonly events: Map<keyof EventMap, Set<EventListener<unknown>>> = new Map()
public addListener<K extends keyof EventMap>(eventName: K, listener: EventListener<EventMap[ K ]>): void {
const eventSet = this.events.get(eventName)
if (eventSet === undefined) {
this.events.set(eventName, new Set([ listener ]) as Set<EventListener<unknown>>)
} else {
eventSet.add(listener as EventListener<unknown>)
}
}
public removeListener<K extends keyof EventMap>(eventName: K, listener: EventListener<EventMap[ K ]>): void {
const eventSet = this.events.get(eventName)
if (eventSet === undefined) return
eventSet.delete(listener as EventListener<unknown>)
if (eventSet.size === 0) {
this.events.delete(eventName)
}
}
on = this.addListener
off = this.removeListener
public emit<K extends keyof EventMap>(eventName: K, event: EventMap[ K ]): void {
this.events.get(eventName)?.forEach((listener: EventListener<EventMap[ K ]>) => {
listener.apply(this, [ event ])
})
}
}