Emitter: use Set for "once"

Refs: #267
Refs: #293
Refs: #291

Author: tshemsedinov

lib/events.js

@@ -89,31 +89,36 @@ class Emitter {
     }
     const on = event.on.slice();
     const promises = on.map(async (fn) => fn(value));
-    if (event.once.length > 0) {
-      const on = new Array(event.on.length);
+    if (event.once.size > 0) {
+      const len = event.on.length;
+      const on = new Array(len);
       let index = 0;
-      for (let i = 0, len = event.on.length; i < len; i++) {
+      for (let i = 0; i < len; i++) {
         const listener = event.on[i];
-        if (!event.once.includes(listener)) on[index++] = listener;
+        if (!event.once.has(listener)) on[index++] = listener;
+      }
+      if (index === 0) {
+        this.#events.delete(eventName);
+        return Promise.resolve();
       }
       on.length = index;
-      if (index > 0) this.#events.set(eventName, { on, once: [] });
-      else this.#events.delete(eventName);
+      this.#events.set(eventName, { on, once: new Set() });
     }
     return Promise.all(promises).then(() => undefined);
   }
 
   #addListener(eventName, listener, once) {
     let event = this.#events.get(eventName);
     if (!event) {
-      event = { on: [listener], once: once ? [listener] : [] };
+      const on = [listener];
+      event = { on, once: once ? new Set(on) : new Set() };
       this.#events.set(eventName, event);
     } else {
       if (event.on.includes(listener)) {
         throw new Error('Duplicate listeners detected');
       }
       event.on.push(listener);
-      if (once) event.once.push(listener);
+      if (once) event.once.add(listener);
     }
     if (event.on.length > this.#maxListeners) {
       throw new Error(
@@ -135,10 +140,9 @@ class Emitter {
     if (!listener) return void this.#events.delete(eventName);
     const event = this.#events.get(eventName);
     if (!event) return;
-    const onIndex = event.on.indexOf(listener);
-    if (onIndex > -1) event.on.splice(onIndex, 1);
-    const onceIndex = event.once.indexOf(listener);
-    if (onceIndex > -1) event.once.splice(onceIndex, 1);
+    const index = event.on.indexOf(listener);
+    if (index > -1) event.on.splice(index, 1);
+    event.once.delete(listener);
   }
 
   toPromise(eventName) {
@@ -157,31 +161,15 @@ class Emitter {
   }
 
   listeners(eventName) {
-    if (eventName) {
-      const event = this.#events.get(eventName);
-      return event ? event.on : [];
-    }
-    const listeners = new Set();
-    for (const event of this.#events.values()) {
-      for (let i = 0, len = event.on.length; i < len; i++) {
-        listeners.add(event.on[i]);
-      }
-    }
-    return Array.from(listeners);
+    if (!eventName) throw new Error('Expected eventName');
+    const event = this.#events.get(eventName);
+    return event ? event.on : [];
   }
 
   listenerCount(eventName) {
-    if (eventName) {
-      const event = this.#events.get(eventName);
-      return event ? event.on.length : 0;
-    }
-    const listeners = new Set();
-    for (const event of this.#events.values()) {
-      for (let i = 0, len = event.on.length; i < len; i++) {
-        listeners.add(event.on[i]);
-      }
-    }
-    return listeners.size;
+    if (!eventName) throw new Error('Expected eventName');
+    const event = this.#events.get(eventName);
+    return event ? event.on.length : 0;
   }
 
   eventNames() {

metautil.d.ts

@@ -307,7 +307,7 @@ export class Emitter {
   toAsyncIterable(eventName: EventName): AsyncIterable<unknown>;
 
   clear(eventName?: EventName): void;
-  listeners(eventName?: EventName): Listener[];
-  listenerCount(eventName?: EventName): number;
+  listeners(eventName: EventName): Listener[];
+  listenerCount(eventName: EventName): number;
   eventNames(): EventName[];
 }