Add EventEmitter.prototype.once

lib/events.js

@@ -76,6 +76,14 @@ EventEmitter.prototype.addListener = function (type, listener) {
 
 EventEmitter.prototype.on = EventEmitter.prototype.addListener;
 
+EventEmitter.prototype.once = function (type, listener) {
+  var self = this;
+  self.on(type, function g () {
+    self.removeListener(type, g);
+    listener.apply(this, arguments);
+  });
+};
+
 EventEmitter.prototype.removeListener = function (type, listener) {
   if ('function' !== typeof listener) {
     throw new Error('removeListener only takes instances of Function');

test/simple/test-event-emitter-once.js

@@ -0,0 +1,20 @@
+common = require("../common");
+assert = common.assert
+var events = require('events');
+
+var e = new events.EventEmitter();
+var times_hello_emited = 0;
+
+e.once("hello", function (a, b) {
+  times_hello_emited++;
+});
+
+e.emit("hello", "a", "b");
+e.emit("hello", "a", "b");
+e.emit("hello", "a", "b");
+e.emit("hello", "a", "b");
+
+process.addListener("exit", function () {
+  assert.equal(1, times_hello_emited);
+});
+