Add type for conveniently typing mixin objects

index.d.ts

@@ -79,3 +79,27 @@ export interface Emitter<Events extends EventsMap = DefaultEvents> {
 export function createNanoEvents<
   Events extends EventsMap = DefaultEvents
 >(): Emitter<Events>
+
+/**
+ * An interface for mixins that expose the `on` function (without the emitter
+ * bound to `this`)
+ *
+ * ```js
+ * import { createNanoEvents } from 'nanoevents'
+ *
+ * class Ticker implements EmitterMixin<Events> {
+ *   constructor() {
+ *     this.emitter = createNanoEvents()
+ *   }
+ *   on(...args) {
+ *     return this.emitter.on(...args)
+ *   }
+ *   tick() {
+ *     this.emitter.emit('tick')
+ *   }
+ * }
+ * ```
+ */
+export interface EmitterMixin<Events extends EventsMap = DefaultEvents> {
+  on<K extends keyof Events>(event: K, cb: Events[K]): Unsubscribe
+}

test/types.ts

@@ -1,4 +1,4 @@
-import type { Emitter } from '../index.js';
+import type { Emitter, EmitterMixin } from '../index.js';
 import { createNanoEvents } from '../index.js'
 
 interface Events {
@@ -37,3 +37,26 @@ function listenersCount(emitter: Emitter): number {
 }
 
 console.log(listenersCount(ee))
+
+type Mixin = {
+  add: () => void
+} & EmitterMixin<Events>
+
+const createMixin = (): Mixin => {
+  let mixinEmitter = createNanoEvents<Events>()
+
+  return {
+    add: () => {
+      mixinEmitter.emit('add', 1)
+    },
+    on: mixinEmitter.on.bind(mixinEmitter),
+  }
+}
+
+const mixin = createMixin()
+
+mixin.on('add', (a) => {
+  console.log(a)
+})
+
+mixin.add()