stream: improve webstream readable async iterator performance

PR-URL: #49662
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>

Author: rluvaton

lib/internal/webstreams/readablestream.js

@@ -479,9 +479,13 @@ class ReadableStream {
 
 // eslint-disable-next-line no-use-before-define
 constreader=newReadableStreamDefaultReader(this);
-letdone=false;
+
+// No __proto__ here to avoid the performance hit.
+conststate={
+done: false,
+current: undefined,
+};
 letstarted=false;
-letcurrent;
 
 // The nextSteps function is not an async function in order
 // to make it more efficient. Because nextSteps explicitly
@@ -490,7 +494,7 @@ class ReadableStream {
 // unnecessary Promise allocations to occur, which just add
 // cost.
 functionnextSteps(){
-if(done)
+if(state.done)
 returnPromiseResolve({done: true,value: undefined});
 
 if(reader[kState].stream===undefined){
@@ -500,31 +504,15 @@ class ReadableStream {
 }
 constpromise=createDeferredPromise();
 
-readableStreamDefaultReaderRead(reader,{
-[kChunk](chunk){
-current=undefined;
-promise.resolve({value: chunk,done: false});
-},
-[kClose](){
-current=undefined;
-done=true;
-readableStreamReaderGenericRelease(reader);
-promise.resolve({done: true,value: undefined});
-},
-[kError](error){
-current=undefined;
-done=true;
-readableStreamReaderGenericRelease(reader);
-promise.reject(error);
-},
-});
+// eslint-disable-next-line no-use-before-define
+readableStreamDefaultReaderRead(reader,newReadableStreamAsyncIteratorReadRequest(reader,state,promise));
 returnpromise.promise;
 }
 
 asyncfunctionreturnSteps(value){
-if(done)
+if(state.done)
 return{done: true, value };// eslint-disable-line node-core/avoid-prototype-pollution
-done=true;
+state.done=true;
 
 if(reader[kState].stream===undefined){
 thrownewERR_INVALID_STATE.TypeError(
@@ -561,19 +549,19 @@ class ReadableStream {
 // need to investigate if it's a bug in our impl or
 // the spec.
 if(!started){
-current=PromiseResolve();
+state.current=PromiseResolve();
 started=true;
 }
-current=current!==undefined ?
-PromisePrototypeThen(current,nextSteps,nextSteps) :
+state.current=state.current!==undefined ?
+PromisePrototypeThen(state.current,nextSteps,nextSteps) :
 nextSteps();
-returncurrent;
+returnstate.current;
 },
 
 return(error){
-returncurrent ?
+returnstate.current ?
 PromisePrototypeThen(
-current,
+state.current,
 ()=>returnSteps(error),
 ()=>returnSteps(error)) :
 returnSteps(error);
@@ -774,6 +762,33 @@ function createReadableStreamBYOBRequest(controller, view) {
 returnstream;
 }
 
+classReadableStreamAsyncIteratorReadRequest{
+constructor(reader,state,promise){
+this.reader=reader;
+this.state=state;
+this.promise=promise;
+}
+
+[kChunk](chunk){
+this.state.current=undefined;
+this.promise.resolve({value: chunk,done: false});
+}
+
+[kClose](){
+this.state.current=undefined;
+this.state.done=true;
+readableStreamReaderGenericRelease(this.reader);
+this.promise.resolve({done: true,value: undefined});
+}
+
+[kError](error){
+this.state.current=undefined;
+this.state.done=true;
+readableStreamReaderGenericRelease(this.reader);
+this.promise.reject(error);
+}
+}
+
 classDefaultReadRequest{
 constructor(){
 this[kState]=createDeferredPromise();