[feature] Add support for objets with a handleEvent() method

Make `WebSocket.prototype.addEventListener()` support an event listener
specified as an object with a `handleEvent()` method.

Fixes #2092

doc/ws.md

@@ -426,7 +426,7 @@ handshake. This allows you to read headers from the server, for example
 ### websocket.addEventListener(type, listener[, options])
 
 - `type` {String} A string representing the event type to listen for.
-- `listener` {Function} The listener to add.
+- `listener` {Function|Object} The listener to add.
 - `options` {Object}
   - `once` {Boolean} A `Boolean` indicating that the listener should be invoked
     at most once after being added. If `true`, the listener would be
@@ -555,7 +555,7 @@ The current state of the connection. This is one of the ready state constants.
 ### websocket.removeEventListener(type, listener)
 
 - `type` {String} A string representing the event type to remove.
-- `listener` {Function} The listener to remove.
+- `listener` {Function|Object} The listener to remove.
 
 Removes an event listener emulating the `EventTarget` interface. This method
 only removes listeners added with

lib/event-target.js

@@ -178,7 +178,7 @@ const EventTarget = {
    * Register an event listener.
    *
    * @param {String} type A string representing the event type to listen for
-   * @param {Function} listener The listener to add
+   * @param {(Function|Object)} listener The listener to add
    * @param {Object} [options] An options object specifies characteristics about
    *     the event listener
    * @param {Boolean} [options.once=false] A `Boolean` indicating that the
@@ -196,7 +196,7 @@ const EventTarget = {
         });
 
         event[kTarget] = this;
-        listener.call(this, event);
+        callListener(listener, this, event);
       };
     } else if (type === 'close') {
       wrapper = function onClose(code, message) {
@@ -207,7 +207,7 @@ const EventTarget = {
         });
 
         event[kTarget] = this;
-        listener.call(this, event);
+        callListener(listener, this, event);
       };
     } else if (type === 'error') {
       wrapper = function onError(error) {
@@ -217,14 +217,14 @@ const EventTarget = {
         });
 
         event[kTarget] = this;
-        listener.call(this, event);
+        callListener(listener, this, event);
       };
     } else if (type === 'open') {
       wrapper = function onOpen() {
         const event = new Event('open');
 
         event[kTarget] = this;
-        listener.call(this, event);
+        callListener(listener, this, event);
       };
     } else {
       return;
@@ -244,7 +244,7 @@ const EventTarget = {
    * Remove an event listener.
    *
    * @param {String} type A string representing the event type to remove
-   * @param {Function} handler The listener to remove
+   * @param {(Function|Object)} handler The listener to remove
    * @public
    */
   removeEventListener(type, handler) {
@@ -264,3 +264,19 @@ module.exports = {
   EventTarget,
   MessageEvent
 };
+
+/**
+ * Call an event listener
+ *
+ * @param {(Function|Object)} listener The listener to call
+ * @param {*} thisArg The value to use as `this`` when calling the listener
+ * @param {Event} event The event to pass to the listener
+ * @private
+ */
+function callListener(listener, thisArg, event) {
+  if (typeof listener === 'object' && listener.handleEvent) {
+    listener.handleEvent.call(listener, event);
+  } else {
+    listener.call(thisArg, event);
+  }
+}

test/websocket.test.js

@@ -3264,14 +3264,15 @@ describe('WebSocket', () => {
 
       assert.strictEqual(ws.listenerCount('open'), 1);
 
-      ws.addEventListener(
-        'message',
-        () => {
+      const listener = {
+        handleEvent() {
           events.push('message');
+          assert.strictEqual(this, listener);
           assert.strictEqual(ws.listenerCount('message'), 0);
-        },
-        { once: true }
-      );
+        }
+      };
+
+      ws.addEventListener('message', listener, { once: true });
 
       assert.strictEqual(ws.listenerCount('message'), 1);
 
@@ -3318,17 +3319,19 @@ describe('WebSocket', () => {
     it('supports the `removeEventListener` method', () => {
       const ws = new WebSocket('ws://localhost', { agent: new CustomAgent() });
 
-      ws.addEventListener('message', NOOP);
+      const listener = { handleEvent() {} };
+
+      ws.addEventListener('message', listener);
       ws.addEventListener('open', NOOP);
 
-      assert.strictEqual(ws.listeners('message')[0][kListener], NOOP);
+      assert.strictEqual(ws.listeners('message')[0][kListener], listener);
       assert.strictEqual(ws.listeners('open')[0][kListener], NOOP);
 
       ws.removeEventListener('message', () => {});
 
-      assert.strictEqual(ws.listeners('message')[0][kListener], NOOP);
+      assert.strictEqual(ws.listeners('message')[0][kListener], listener);
 
-      ws.removeEventListener('message', NOOP);
+      ws.removeEventListener('message', listener);
       ws.removeEventListener('open', NOOP);
 
       assert.strictEqual(ws.listenerCount('message'), 0);