From 50c7d80fb0c5c8c13ce8755e1be54c1fd5543748 Mon Sep 17 00:00:00 2001
From: isaacs <i@izs.me>
Date: Sat, 4 Aug 2012 13:32:18 -0700
Subject: [PATCH] events: emitter.listeners() should not have side effects

Fixes #3803
---
 lib/events.js                                 |  5 +-
 ...st-event-emitter-listeners-side-effects.js | 61 +++++++++++++++++++
 2 files changed, 63 insertions(+), 3 deletions(-)
 create mode 100644 test/simple/test-event-emitter-listeners-side-effects.js

diff --git a/lib/events.js b/lib/events.js
index 9778960f9da..9b26c566306 100644
--- a/lib/events.js
+++ b/lib/events.js
@@ -237,10 +237,9 @@ EventEmitter.prototype.removeAllListeners = function(type) {
 };
 
 EventEmitter.prototype.listeners = function(type) {
-  if (!this._events) this._events = {};
-  if (!this._events[type]) this._events[type] = [];
+  if (!this._events || !this._events[type]) return [];
   if (!isArray(this._events[type])) {
-    this._events[type] = [this._events[type]];
+    return [this._events[type]];
   }
   return this._events[type].slice(0);
 };
diff --git a/test/simple/test-event-emitter-listeners-side-effects.js b/test/simple/test-event-emitter-listeners-side-effects.js
new file mode 100644
index 00000000000..af725beed62
--- /dev/null
+++ b/test/simple/test-event-emitter-listeners-side-effects.js
@@ -0,0 +1,61 @@
+
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common');
+var assert = require('assert');
+var events = require('events');
+
+var EventEmitter = require('events').EventEmitter;
+var assert = require('assert');
+
+var e = new EventEmitter;
+var fl;  // foo listeners
+
+fl = e.listeners('foo');
+assert(Array.isArray(fl));
+assert(fl.length === 0);
+assert(typeof e._events == 'undefined');
+
+e.on('foo', assert.fail);
+fl = e.listeners('foo');
+assert(e._events.foo === assert.fail);
+assert(Array.isArray(fl));
+assert(fl.length === 1);
+assert(fl[0] === assert.fail);
+
+e.listeners('bar');
+assert(!e._events.hasOwnProperty('bar'));
+
+e.on('foo', assert.ok);
+fl = e.listeners('foo');
+
+assert(Array.isArray(e._events.foo));
+assert(e._events.foo.length === 2);
+assert(e._events.foo[0] === assert.fail);
+assert(e._events.foo[1] === assert.ok);
+
+assert(Array.isArray(fl));
+assert(fl.length === 2);
+assert(fl[0] === assert.fail);
+assert(fl[1] === assert.ok);
+
+console.log('ok');