perf: cool off EventEmitters

TODO.md

@@ -12,7 +12,7 @@
 - ✔ Eliminate immutable.toJS()
 - ✔ Track dirty entity state (entityList.tick())
 - ✔ Investigate visibleEntities path
-- ❌ Investigate lookupEmitListeners path
+- ✔ Investigate lookupEmitListeners path
 - ❌ Investigate visibleBoundingBoxes path
-- ❌ EventEmitter::emit is too hot
+- ✔ EventEmitter::emit is too hot
 - ❌ entityList.fromJSON()

packages/mixins/event-emitter.js

@@ -25,7 +25,8 @@ export function EventEmitterMixin(Superclass) {
         return;
       }
 
-      for (const {once, type, namespace, fn, bound, that} of listeners) {
+      for (let i = 0; i < listeners.length; ++i) {
+        const {once, type, namespace, fn, bound, that} = listeners[i];
         const offset = type !== '*' ? 1 : 0;
 
         if (once) {
@@ -86,10 +87,7 @@ export function EventEmitterMixin(Superclass) {
 
     lookupEmitListeners(type) {
       return ['*', type].reduce((r, type) => {
-        if (type in this.$$events) {
-          r.push(...this.$$events[type]);
-        }
-        return r;
+        return r.concat(type in this.$$events ? this.$$events[type] : []);
       }, []);
     }