feat: once

app/lib/event-emitter.js

@@ -2,19 +2,22 @@ import fastCall from './fast-call.js';
 
 export default class EventEmitter {
   $$listeners = {};
-  addListener(type, listener) {
+  addListener(type, listener, options = {}) {
     if (!this.$$listeners[type]) {
-      this.$$listeners[type] = new Set();
+      this.$$listeners[type] = new Map();
     }
-    this.$$listeners[type].add(listener);
+    this.$$listeners[type].set(listener, options);
   }
   invoke(type, ...args) {
     const listeners = this.$$listeners[type];
     if (!listeners) {
       return;
     }
-    for (const listener of listeners) {
+    for (const [listener, options] of listeners) {
       fastCall(listener, undefined, args);
+      if (options.once) {
+        listeners.delete(listener);
+      }
     }
   }
   removeListener(type, listener) {