feat: Add new @n8n/utils package (no-changelog) (#13536)

packages/@n8n/utils/src/event-bus.ts

@@ -0,0 +1,84 @@
+// eslint-disable-next-line @typescript-eslint/ban-types
+export type CallbackFn = Function;
+
+type Payloads<ListenerMap> = {
+	[E in keyof ListenerMap]: unknown;
+};
+
+type Listener<Payload> = (payload: Payload) => void;
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export interface EventBus<ListenerMap extends Payloads<ListenerMap> = Record<string, any>> {
+	on<EventName extends keyof ListenerMap & string>(
+		eventName: EventName,
+		fn: Listener<ListenerMap[EventName]>,
+	): void;
+
+	once<EventName extends keyof ListenerMap & string>(
+		eventName: EventName,
+		fn: Listener<ListenerMap[EventName]>,
+	): void;
+
+	off<EventName extends keyof ListenerMap & string>(
+		eventName: EventName,
+		fn: Listener<ListenerMap[EventName]>,
+	): void;
+
+	emit<EventName extends keyof ListenerMap & string>(
+		eventName: EventName,
+		event?: ListenerMap[EventName],
+	): void;
+}
+
+/**
+ * Creates an event bus with the given listener map.
+ *
+ * @example
+ * ```ts
+ * const eventBus = createEventBus<{
+ *   'user-logged-in': { username: string };
+ *   'user-logged-out': never;
+ * }>();
+ */
+export function createEventBus<
+	// eslint-disable-next-line @typescript-eslint/no-explicit-any
+	ListenerMap extends Payloads<ListenerMap> = Record<string, any>,
+>(): EventBus<ListenerMap> {
+	const handlers = new Map<string, CallbackFn[]>();
+
+	return {
+		on(eventName, fn) {
+			let eventFns = handlers.get(eventName);
+			if (!eventFns) {
+				eventFns = [fn];
+			} else {
+				eventFns.push(fn);
+			}
+			handlers.set(eventName, eventFns);
+		},
+
+		once(eventName, fn) {
+			const handler: typeof fn = (payload) => {
+				this.off(eventName, handler);
+				fn(payload);
+			};
+			this.on(eventName, handler);
+		},
+
+		off(eventName, fn) {
+			const eventFns = handlers.get(eventName);
+			if (eventFns) {
+				eventFns.splice(eventFns.indexOf(fn) >>> 0, 1);
+			}
+		},
+
+		emit(eventName, event) {
+			const eventFns = handlers.get(eventName);
+			if (eventFns) {
+				eventFns.slice().forEach((handler) => {
+					handler(event);
+				});
+			}
+		},
+	};
+}