Emittery generic is an eventName->EventData map

examples/typed.ts

@@ -1,17 +1,22 @@
 import Emittery from '../';
 
-type EventType = 'value' | 'end' | 'error';
-
 interface IRecord {
 	msg: string;
 	data?: any[];
 	ts: number;
 }
 
+type EventType = {
+	'value': IRecord,
+	'end': null,
+	'error': Error
+};
+
 class Logger extends Emittery<EventType> {
 
 	log(msg: string, ...data: any[]) {
-		this.emit<IRecord>('value', {msg, data, ts: Date.now()});
+		this.emit('end', null)
+		this.emit('value', {msg, data, ts: Date.now()});
 		console.log(msg, ...data);
 	}
 }
@@ -22,11 +27,11 @@ const logger = new Logger();
 logger.log('Logging', 'foo');
 logger.log('some more', 'bar', 'baz');
 logger.log('finally', 'fooz');
-logger.emitSerial('end');
+logger.emitSerial('end', null);
 
 
 // Register our listeners
-const off = logger.on<IRecord>('value', rec => console.log(`data: ${rec.data}, ts: ${rec.ts}`));
+const off = logger.on('value', rec => console.log(`data: ${rec.data}, ts: ${rec.ts}`));
 
 logger.onAny((name: string, data: any) => console.log('Event %d. Called with %d', name, data));
 

index.d.ts

@@ -7,9 +7,9 @@ export default Emittery;
 /**
  * Simple and modern async event emitter
  *
- * @template T - An union of literal event name.
+ * @template T - Map event name to an event data type.
  */
-declare class Emittery<T extends string> {
+declare class Emittery<T> {
 
 		/**
 		 * Subscribe to an event.
@@ -19,15 +19,15 @@ declare class Emittery<T extends string> {
 		 *
 		 * @returns Unsubscribe method.
 		 */
-		on<U>(eventName: T, listener: (eventData: U) => any): () => void;
+		on<K extends keyof T>(eventName: K, listener: (eventData?: T[K]) => void | Promise<void>): () => void;
 
 		/**
 		 * Subscribe to an event only once. It will be unsubscribed after the first
 		 * event.
 		 *
 		 * @returns Promise for the event data when eventName is emitted
 		 */
-		once<U>(eventName: T): Promise<U>;
+		once<K extends keyof T>(eventName: K): Promise<T[K]>;
 
 		/**
 		 * Unsubscribe to an event.
@@ -37,14 +37,14 @@ declare class Emittery<T extends string> {
 		 *
 		 * @param [listener]
 		 */
-		off(eventName: T, listener?: (x: any) => any): void;
+		off<K extends keyof T>(eventName: K, listener?: (eventData?: T[K]) => any): void;
 
 		/**
 		 * Subscribe to be notified about any event.
 		 *
 		 * @returns A method to unsubscribe
 		 */
-		onAny(listener: (eventName: T, eventData: any) => any): () => void;
+		onAny<K extends keyof T>(listener: (eventName: K, eventData?: T[K]) => any): () => void;
 
 		/**
 		 * Unsubscribe an onAny listener.
@@ -53,7 +53,7 @@ declare class Emittery<T extends string> {
 		 *
 		 * @param [listener]
 		 */
-		offAny(listener?: (eventName: T, eventData: any) => any): void;
+		offAny<K extends keyof T>(listener?: (eventName: K, eventData?: T[K]) => any): void;
 
 		/**
 		 * Trigger an event asynchronously, optionally with some data. Listeners
@@ -68,7 +68,7 @@ declare class Emittery<T extends string> {
 		 *
 		 * @returns A promise for when all the event listeners are done.
 		 */
-		emit<U>(eventName: T, eventData?: U): Promise<void>;
+		emit<K extends keyof T>(eventName: K, eventData?: T[K]): Promise<void>;
 
 		/**
 		 * Same as `emit`, but it waits for each listener to resolve before
@@ -80,7 +80,7 @@ declare class Emittery<T extends string> {
 		 *
 		 * @returns A promise for the last event listener settle or first one rejecting.
 		 */
-		emitSerial<U>(eventName: T, eventData?: U): Promise<void>;
+		emitSerial<K extends keyof T>(eventName: K, eventData?: T[K]): Promise<void>;
 
 		/**
 		 * Clear all event listeners on the instance.
@@ -93,5 +93,5 @@ declare class Emittery<T extends string> {
 		 * @param eventName
 		 * @returns Listener count.
 		 */
-		listenerCount(eventName?: T): number;
+		listenerCount(eventName?: keyof T): number;
 }