Method on

nodejs/src/session.ts:403–430

(
        eventTypeOrHandler: K | SessionEventHandler,
        handler?: TypedSessionEventHandler<K>
    )

    on(handler: SessionEventHandler): () => void;

    on<K extends SessionEventType>(
        eventTypeOrHandler: K | SessionEventHandler,
        handler?: TypedSessionEventHandler<K>
    ): () => void {
        // Overload 1: on(eventType, handler) - typed event subscription
        if (typeof eventTypeOrHandler === "string" && handler) {
            const eventType = eventTypeOrHandler;
            if (!this.typedEventHandlers.has(eventType)) {
                this.typedEventHandlers.set(eventType, new Set());
            }
            // Cast is safe: handler receives the correctly typed event at dispatch time
            const storedHandler = handler as (event: SessionEvent) => void;
            this.typedEventHandlers.get(eventType)!.add(storedHandler);
            return () => {
                const handlers = this.typedEventHandlers.get(eventType);
                if (handlers) {
                    handlers.delete(storedHandler);
                }
            };
        }

        // Overload 2: on(handler) - wildcard subscription
        const wildcardHandler = eventTypeOrHandler as SessionEventHandler;
        this.eventHandlers.add(wildcardHandler);
        return () => {
            this.eventHandlers.delete(wildcardHandler);
        };
    }

    /**
     * Dispatches an event to all registered handlers.