stream: fix eventNames() to not return not defined events

PR-URL: #51331 Reviewed-By: Benjamin Gruenbaum <[email protected]> Reviewed-By: Stephen Belanger <[email protected]> Reviewed-By: Luigi Pinca <[email protected]>

Author: IlyasShabi

lib/internal/streams/legacy.js

@@ -3,6 +3,7 @@
 const{
  ArrayIsArray,
  ObjectSetPrototypeOf,
+ ReflectOwnKeys,
 }=primordials;
 
 constEE=require('events');
@@ -93,6 +94,16 @@ Stream.prototype.pipe = function(dest, options){
 returndest;
 };
 
+Stream.prototype.eventNames=functioneventNames(){
+constnames=[];
+for(constkeyofReflectOwnKeys(this._events)){
+if(typeofthis._events[key]==='function'||(ArrayIsArray(this._events[key])&&this._events[key].length>0)){
+names.push(key);
+}
+}
+returnnames;
+};
+
 functionprependListener(emitter,event,fn){
 // Sadly this is not cacheable as some libraries bundle their own
 // event emitter implementation with them.

test/parallel/test-stream-event-names.js

@@ -0,0 +1,42 @@
+'use strict';
+
+require('../common');
+constassert=require('assert');
+const{ Readable, Writable, Duplex }=require('stream');
+
+{
+conststream=newReadable();
+assert.strictEqual(stream.eventNames().length,0);
+}
+
+{
+conststream=newReadable();
+stream.on('foo',()=>{});
+stream.on('data',()=>{});
+stream.on('error',()=>{});
+assert.deepStrictEqual(stream.eventNames(),['error','data','foo']);
+}
+
+{
+conststream=newWritable();
+assert.strictEqual(stream.eventNames().length,0);
+}
+
+{
+conststream=newWritable();
+stream.on('foo',()=>{});
+stream.on('drain',()=>{});
+stream.on('prefinish',()=>{});
+assert.deepStrictEqual(stream.eventNames(),['prefinish','drain','foo']);
+}
+{
+conststream=newDuplex();
+assert.strictEqual(stream.eventNames().length,0);
+}
+
+{
+conststream=newDuplex();
+stream.on('foo',()=>{});
+stream.on('finish',()=>{});
+assert.deepStrictEqual(stream.eventNames(),['finish','foo']);
+}