events: support event handlers

PR-URL: https://github.com/nodejs/node/pull/34015
Reviewed-By: Denys Otrishko <shishugi@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

1 files changed, 19 insertions, 2 deletions

diff --git a/lib/internal/event_target.js b/lib/internal/event_target.js
index 7c34acd5c5d..9fef64aaba2 100644
--- a/lib/internal/event_target.js
+++ b/lib/internal/event_target.js
@@ -479,10 +479,27 @@ function emitUnhandledRejectionOrErr(that, err, event) {
   process.emit('error', err, event);
 }
 
-// EventEmitter-ish API:
-
+function defineEventHandler(emitter, name) {
+  // 8.1.5.1 Event handlers - basically `on[eventName]` attributes
+  let eventHandlerValue;
+  Object.defineProperty(emitter, `on${name}`, {
+    get() {
+      return eventHandlerValue;
+    },
+    set(value) {
+      if (eventHandlerValue) {
+        emitter.removeEventListener(name, eventHandlerValue);
+      }
+      if (typeof value === 'function') {
+        emitter.addEventListener(name, value);
+      }
+      eventHandlerValue = value;
+    }
+  });
+}
 module.exports = {
   Event,
   EventTarget,
   NodeEventTarget,
+  defineEventHandler,
 };