stream: make a number of cleanups in broadcast.js

Author: jasnell

lib/internal/streams/iter/broadcast.js

@@ -15,6 +15,7 @@ const {
   Promise,
   PromisePrototypeThen,
   PromiseResolve,
+  PromiseWithResolvers,
   SafeSet,
   String,
   Symbol,
@@ -56,12 +57,7 @@ const {
   RingBuffer,
 } = require('internal/streams/iter/ringbuffer');
 
-// Cached resolved promise to avoid allocating a new one on every sync fast-path.
 const kResolvedPromise = PromiseResolve();
-
-// Non-exported symbols for internal cross-class communication between
-// BroadcastImpl and BroadcastWriter. Because these symbols are not exported,
-// external code cannot access the internal methods/fields.
 const kCancelWriter = Symbol('cancelWriter');
 const kWrite = Symbol('write');
 const kEnd = Symbol('end');
@@ -163,8 +159,10 @@ class BroadcastImpl {
     const self = this;
 
     return {
+      __proto__: null,
       [SymbolAsyncIterator]() {
         return {
+          __proto__: null,
           async next() {
             if (state.detached) {
               // If detached due to an error, throw the error
@@ -192,10 +190,10 @@ class BroadcastImpl {
               return { __proto__: null, done: true, value: undefined };
             }
 
-            return new Promise((resolve, reject) => {
-              state.resolve = resolve;
-              state.reject = reject;
-            });
+            const { promise, resolve, reject } = PromiseWithResolvers();
+            state.resolve = resolve;
+            state.reject = reject;
+            return promise;
           },
 
           async return() {