events: define event handler as enumerable

PR-URL: #35931
Backport-PR-URL: #38386
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

Author: benjamingr

lib/internal/event_target.js

@@ -591,7 +591,9 @@ function defineEventHandler(emitter, name) {
         emitter.addEventListener(name, value);
       }
       eventHandlerValue = value;
-    }
+    },
+    configurable: true,
+    enumerable: true
   });
 }
 module.exports = {

test/parallel/test-eventtarget.js

@@ -517,3 +517,10 @@ let asyncTest = Promise.resolve();
   }));
   target.dispatchEvent(new Event('foo'));
 }
+{
+  const target = new EventTarget();
+  defineEventHandler(target, 'foo');
+  const descriptor = Object.getOwnPropertyDescriptor(target, 'onfoo');
+  strictEqual(descriptor.configurable, true);
+  strictEqual(descriptor.enumerable, true);
+}