events: add 'removeListener' event

Author: bnoordhuis

doc/api/events.markdown

@@ -26,7 +26,7 @@ If there is no listener for it, then the default action is to print a stack
 trace and exit the program.
 
 All EventEmitters emit the event `'newListener'` when new listeners are
-added.
+added and `'removeListener'` when a listener is removed.
 
 ### emitter.addListener(event, listener)
 ### emitter.on(event, listener)

lib/events.js

@@ -191,6 +191,7 @@ EventEmitter.prototype.once = function(type, listener) {
   return this;
 };
 
+// emits a 'removeListener' event iff the listener was removed
 EventEmitter.prototype.removeListener = function(type, listener) {
   if ('function' !== typeof listener) {
     throw new Error('removeListener only takes instances of Function');
@@ -216,23 +217,41 @@ EventEmitter.prototype.removeListener = function(type, listener) {
     list.splice(position, 1);
     if (list.length == 0)
       delete this._events[type];
+    this.emit('removeListener', type, listener);
   } else if (list === listener ||
              (list.listener && list.listener === listener))
   {
     delete this._events[type];
+    this.emit('removeListener', type, listener);
   }
 
   return this;
 };
 
 EventEmitter.prototype.removeAllListeners = function(type) {
+  if (!this._events) return this;
+
   if (arguments.length === 0) {
+    for (var key in this._events) {
+      if (key === 'removeListener') continue;
+      this.removeAllListeners(key);
+    }
+    this.removeAllListeners('removeListener');
     this._events = {};
     return this;
   }
 
-  // does not use listeners(), so no side effect of creating _events[type]
-  if (type && this._events && this._events[type]) this._events[type] = null;
+  var listeners = this._events[type];
+  if (isArray(listeners)) {
+    while (listeners.length) {
+      // LIFO order
+      this.removeListener(type, listeners[listeners.length - 1]);
+    }
+  } else if (listeners) {
+    this.removeListener(type, listeners);
+  }
+  this._events[type] = null;
+
   return this;
 };
 

test/simple/test-event-emitter-remove-all-listeners.js

@@ -24,6 +24,17 @@ var assert = require('assert');
 var events = require('events');
 
 
+function expect(expected) {
+  var actual = [];
+  process.on('exit', function() {
+    assert.deepEqual(actual.sort(), expected.sort());
+  });
+  function listener(name) {
+    actual.push(name)
+  }
+  return common.mustCall(listener, expected.length);
+}
+
 function listener() {}
 
 var e1 = new events.EventEmitter();
@@ -34,6 +45,7 @@ e1.on('baz', listener);
 var fooListeners = e1.listeners('foo');
 var barListeners = e1.listeners('bar');
 var bazListeners = e1.listeners('baz');
+e1.on('removeListener', expect(['bar', 'baz', 'baz']));
 e1.removeAllListeners('bar');
 e1.removeAllListeners('baz');
 assert.deepEqual(e1.listeners('foo'), [listener]);
@@ -52,6 +64,9 @@ assert.notEqual(e1.listeners('baz'), bazListeners);
 var e2 = new events.EventEmitter();
 e2.on('foo', listener);
 e2.on('bar', listener);
+// expect LIFO order
+e2.on('removeListener', expect(['foo', 'bar', 'removeListener']));
+e2.on('removeListener', expect(['foo', 'bar']));
 e2.removeAllListeners();
 console.error(e2);
 assert.deepEqual([], e2.listeners('foo'));

test/simple/test-event-emitter-remove-listeners.js

@@ -23,7 +23,6 @@ var common = require('../common');
 var assert = require('assert');
 var events = require('events');
 
-
 var count = 0;
 
 function listener1() {
@@ -41,21 +40,45 @@ function listener3() {
   count++;
 }
 
+function remove1() {
+  assert(0);
+}
+
+function remove2() {
+  assert(0);
+}
+
 var e1 = new events.EventEmitter();
 e1.on('hello', listener1);
+e1.on('removeListener', common.mustCall(function(name, cb) {
+  assert.equal(name, 'hello');
+  assert.equal(cb, listener1);
+}));
 e1.removeListener('hello', listener1);
 assert.deepEqual([], e1.listeners('hello'));
 
 var e2 = new events.EventEmitter();
 e2.on('hello', listener1);
+e2.on('removeListener', assert.fail);
 e2.removeListener('hello', listener2);
 assert.deepEqual([listener1], e2.listeners('hello'));
 
 var e3 = new events.EventEmitter();
 e3.on('hello', listener1);
 e3.on('hello', listener2);
+e3.on('removeListener', common.mustCall(function(name, cb) {
+  assert.equal(name, 'hello');
+  assert.equal(cb, listener1);
+}));
 e3.removeListener('hello', listener1);
 assert.deepEqual([listener2], e3.listeners('hello'));
 
-
-
+var e4 = new events.EventEmitter();
+e4.on('removeListener', common.mustCall(function(name, cb) {
+  if (cb !== remove1) return;
+  this.removeListener('quux', remove2);
+  this.emit('quux');
+}, 2));
+e4.on('quux', remove1);
+e4.on('quux', remove2);
+e4.removeListener('quux', remove1);