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events: make .listeners() return a copy
Make EventEmitter.listeners(event) return a copy of the listeners array instead
of the array itself.

Fixes #3442.
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dynajoe authored and bnoordhuis committed Jul 27, 2012
1 parent f692347 commit 20e12e4
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Showing 3 changed files with 53 additions and 17 deletions.
16 changes: 0 additions & 16 deletions doc/api/events.markdown
Expand Up @@ -64,9 +64,6 @@ Remove a listener from the listener array for the specified event.

Removes all listeners, or those of the specified event.

Note that this will **invalidate** any arrays that have previously been
returned by `emitter.listeners(event)`.


### emitter.setMaxListeners(n)

Expand All @@ -85,19 +82,6 @@ Returns an array of listeners for the specified event.
});
console.log(util.inspect(server.listeners('connection'))); // [ [Function] ]

This array **may** be a mutable reference to the same underlying list of
listeners that is used by the event subsystem. However, certain
actions (specifically, removeAllListeners) will invalidate this
reference.

If you would like to get a copy of the listeners at a specific point in
time that is guaranteed not to change, make a copy, for example by doing
`emitter.listeners(event).slice(0)`.

In a future release of node, this behavior **may** change to always
return a copy, for consistency. In your programs, please do not rely on
being able to modify the EventEmitter listeners using array methods.
Always use the 'on' method to add new listeners.

### emitter.emit(event, [arg1], [arg2], [...])

Expand Down
2 changes: 1 addition & 1 deletion lib/events.js
Expand Up @@ -242,5 +242,5 @@ EventEmitter.prototype.listeners = function(type) {
if (!isArray(this._events[type])) {
this._events[type] = [this._events[type]];
}
return this._events[type];
return this._events[type].slice(0);
};
52 changes: 52 additions & 0 deletions test/simple/test-event-emitter-listeners.js
@@ -0,0 +1,52 @@

// 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');

function listener() {}
function listener2() {}

var e1 = new events.EventEmitter();
e1.on('foo', listener);
var fooListeners = e1.listeners('foo');
assert.deepEqual(e1.listeners('foo'), [listener]);
e1.removeAllListeners('foo');
assert.deepEqual(e1.listeners('foo'), []);
assert.deepEqual(fooListeners, [listener]);

var e2 = new events.EventEmitter();
e2.on('foo', listener);
var e2ListenersCopy = e2.listeners('foo');
assert.deepEqual(e2ListenersCopy, [listener]);
assert.deepEqual(e2.listeners('foo'), [listener]);
e2ListenersCopy.push(listener2);
assert.deepEqual(e2.listeners('foo'), [listener]);
assert.deepEqual(e2ListenersCopy, [listener, listener2]);

var e3 = new events.EventEmitter();
e3.on('foo', listener);
var e3ListenersCopy = e3.listeners('foo');
e3.on('foo', listener2);
assert.deepEqual(e3.listeners('foo'), [listener, listener2]);
assert.deepEqual(e3ListenersCopy, [listener]);

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