console-display: Symbol.toStringTag NOT work when extends EventTarget

Version: v16.0.0-pre
Platform: linux
Subsystem: ubuntu

What steps will reproduce the bug?

     //worked, no extends
     class ET  {
        #tag = "empty"
        constructor(tag) {
              this.#tag = tag
        }
        get [Symbol.toStringTag]() {return(this.#tag)}
     } 
     
     > var et = new ET("uuid-xxxx")
     > et
     ET [uuid-xxxx] {}                     //I want this effect 
     >
     
     
     
     //not work , when extends 
     class ETWithSig extends EventTarget {
        #tag = "empty"
        constructor(tag) {
              super();
              this.#tag = tag
        }
        get [Symbol.toStringTag]() {return(this.#tag)}
     }
     
     
     > var xt = new ETWithSig("uuid-yyyy")
     > xt
     ETWithSig {}                          //not-work when extends 
     >

How often does it reproduce? Is there a required condition?

always

What is the expected behavior?

see the reproduce worked-example

What do you see instead?

see the reproduce extends-example

@nodejs/util

It's an issue with the custom inspect function defined for the EventTarget. These rarely mimic the regular inspect behavior.

I put together a "fix" but we have to be aware that it's more like a bandage. There could be way more things that do not work as expected due to not being the actual object inspected.

Anyone may feel free to open a PR with this change.

diff --git a/lib/internal/event_target.js b/lib/internal/event_target.js
index fe588088cc..92eb22f8cd 100644
--- a/lib/internal/event_target.js
+++ b/lib/internal/event_target.js
@@ -8,6 +8,9 @@ const {
   FunctionPrototypeCall,
   NumberIsInteger,
   ObjectAssign,
+  ObjectCreate,
+  ObjectSetPrototypeOf,
+  ObjectGetPrototypeOf,
   ObjectDefineProperties,
   ObjectDefineProperty,
   ObjectGetOwnPropertyDescriptor,
@@ -32,7 +35,11 @@ const {
 } = require('internal/errors');
 const { validateObject, validateString } = require('internal/validators');
 
-const { customInspectSymbol } = require('internal/util');
+const {
+  getConstructorOf,
+  customInspectSymbol
+} = require('internal/util');
+
 const { inspect } = require('util');
 
 const kIsEventTarget = SymbolFor('nodejs.event_target');
@@ -109,15 +116,14 @@ class Event {
   }
 
   [customInspectSymbol](depth, options) {
-    const name = this.constructor.name;
     if (depth < 0)
-      return name;
+      return this;
 
     const opts = ObjectAssign({}, options, {
       depth: NumberIsInteger(options.depth) ? options.depth - 1 : options.depth
     });
 
-    return `${name} ${inspect({
+    return `${this.constructor.name} ${inspect({
       type: this[kType],
       defaultPrevented: this[kDefaultPrevented],
       cancelable: this[kCancelable],
@@ -435,16 +441,30 @@ class EventTarget {
   [kCreateEvent](nodeValue, type) {
     return new NodeCustomEvent(type, { detail: nodeValue });
   }
+
   [customInspectSymbol](depth, options) {
-    const name = this.constructor.name;
     if (depth < 0)
-      return name;
+      return this;
 
-    const opts = ObjectAssign({}, options, {
+    const opts = {
+      ...options,
       depth: NumberIsInteger(options.depth) ? options.depth - 1 : options.depth
-    });
+    };
+
+    const constructor = getConstructorOf(this) || EventTarget;
+    const object = ObjectCreate({ constructor });
+    ObjectSetPrototypeOf(object, ObjectGetPrototypeOf(this));
+    ObjectDefineProperty(
+      object,
+      SymbolToStringTag,
+      {
+        value: this[SymbolToStringTag],
+        enumerable: false,
+        writable: true
+      }
+    );
 
-    return `${name} ${inspect({}, opts)}`;
+    return inspect(object, opts);
   }
 }

Just wondering - what are you doing with EventTarget?

@benjamingr

@benjamingr
in my application:

I need to make the each AST-NODE (from babel parse result) is a event-target,
and a unique-tag is assigned(for log-collection to log-database-server) .
using Symbol.toStringTag is just for console-manual-debug .

It is a automation testbed for javascripts.

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This issue has been automatically closed after 30 days of inactivity following its stale status (no activity for a total of 120 days).
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console-display: Symbol.toStringTag NOT work when extends EventTarget #37329

What steps will reproduce the bug?

How often does it reproduce? Is there a required condition?

What is the expected behavior?

What do you see instead?

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console-display: Symbol.toStringTag NOT work when extends EventTarget #37329

Description

What steps will reproduce the bug?

How often does it reproduce? Is there a required condition?

What is the expected behavior?

What do you see instead?

Activity

targos commented on Feb 12, 2021

BridgeAR commented on Feb 12, 2021

BridgeAR commented on Feb 12, 2021

benjamingr commented on Feb 12, 2021

navegador5 commented on Feb 13, 2021

github-actions commented on Jun 27, 2026

github-actions commented on Jul 28, 2026

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