events: remove emit micro-optimizations

With improvements in V8, using separate emit functions is no longer
necessary and can instead be replaced by the spread operator.

improvement                             confidence        p.value
events/ee-emit.js n=2000000                 2.98 %        0.09852489
events/ee-emit-2-args.js n=2000000          4.19 %    *** 0.0001914216
events/ee-emit-6-args.js n=2000000         61.69 %    *** 6.611964e-35
events/ee-emit-diff-args.js n=2000000      -0.36 %        0.305069
events/ee-once.js n=20000000                6.42 %    *** 1.27831e-06

benchmark/events/ee-emit-4-args.js

@@ -0,0 +1,20 @@
+'use strict';
+const common = require('../common.js');
+const EventEmitter = require('events').EventEmitter;
+
+const bench = common.createBenchmark(main, { n: [2e6] });
+
+function main(conf) {
+  const n = conf.n | 0;
+
+  const ee = new EventEmitter();
+
+  for (var k = 0; k < 10; k += 1)
+    ee.on('dummy', function() {});
+
+  bench.start();
+  for (var i = 0; i < n; i += 1) {
+    ee.emit('dummy', 5, true, 'something', false);
+  }
+  bench.end(n);
+}

lib/events.js

@@ -105,63 +105,6 @@ EventEmitter.prototype.getMaxListeners = function getMaxListeners() {
   return $getMaxListeners(this);
 };
 
-// These standalone emit* functions are used to optimize calling of event
-// handlers for fast cases because emit() itself often has a variable number of
-// arguments and can be deoptimized because of that. These functions always have
-// the same number of arguments and thus do not get deoptimized, so the code
-// inside them can execute faster.
-function emitNone(handler, isFn, self) {
-  if (isFn)
-    handler.call(self);
-  else {
-    var len = handler.length;
-    var listeners = arrayClone(handler, len);
-    for (var i = 0; i < len; ++i)
-      listeners[i].call(self);
-  }
-}
-function emitOne(handler, isFn, self, arg1) {
-  if (isFn)
-    handler.call(self, arg1);
-  else {
-    var len = handler.length;
-    var listeners = arrayClone(handler, len);
-    for (var i = 0; i < len; ++i)
-      listeners[i].call(self, arg1);
-  }
-}
-function emitTwo(handler, isFn, self, arg1, arg2) {
-  if (isFn)
-    handler.call(self, arg1, arg2);
-  else {
-    var len = handler.length;
-    var listeners = arrayClone(handler, len);
-    for (var i = 0; i < len; ++i)
-      listeners[i].call(self, arg1, arg2);
-  }
-}
-function emitThree(handler, isFn, self, arg1, arg2, arg3) {
-  if (isFn)
-    handler.call(self, arg1, arg2, arg3);
-  else {
-    var len = handler.length;
-    var listeners = arrayClone(handler, len);
-    for (var i = 0; i < len; ++i)
-      listeners[i].call(self, arg1, arg2, arg3);
-  }
-}
-
-function emitMany(handler, isFn, self, args) {
-  if (isFn)
-    handler.apply(self, args);
-  else {
-    var len = handler.length;
-    var listeners = arrayClone(handler, len);
-    for (var i = 0; i < len; ++i)
-      listeners[i].apply(self, args);
-  }
-}
-
 EventEmitter.prototype.emit = function emit(type, ...args) {
   let doError = (type === 'error');
 
@@ -212,22 +155,13 @@ EventEmitter.prototype.emit = function emit(type, ...args) {
     needDomainExit = true;
   }
 
-  const isFn = typeof handler === 'function';
-  switch (args.length) {
-    case 0:
-      emitNone(handler, isFn, this);
-      break;
-    case 1:
-      emitOne(handler, isFn, this, args[0]);
-      break;
-    case 2:
-      emitTwo(handler, isFn, this, args[0], args[1]);
-      break;
-    case 3:
-      emitThree(handler, isFn, this, args[0], args[1], args[2]);
-      break;
-    default:
-      emitMany(handler, isFn, this, args);
+  if (typeof handler === 'function') {
+    handler.apply(this, args);
+  } else {
+    const len = handler.length;
+    const listeners = arrayClone(handler, len);
+    for (var i = 0; i < len; ++i)
+      listeners[i].apply(this, args);
   }
 
   if (needDomainExit)
@@ -313,23 +247,11 @@ EventEmitter.prototype.prependListener =
       return _addListener(this, type, listener, true);
     };
 
-function onceWrapper() {
+function onceWrapper(...args) {
   if (!this.fired) {
     this.target.removeListener(this.type, this.wrapFn);
     this.fired = true;
-    switch (arguments.length) {
-      case 0:
-        return this.listener.call(this.target);
-      case 1:
-        return this.listener.call(this.target, arguments[0]);
-      case 2:
-        return this.listener.call(this.target, arguments[0], arguments[1]);
-      case 3:
-        return this.listener.call(this.target, arguments[0], arguments[1],
-                                  arguments[2]);
-      default:
-        this.listener.apply(this.target, arguments);
-    }
+    this.listener.apply(this.target, args);
   }
 }
 

test/message/stdin_messages.out

@@ -9,10 +9,10 @@ SyntaxError: Strict mode code may not include a with statement
     at Module._compile (module.js:*:*)
     at evalScript (bootstrap_node.js:*:*)
     at Socket.<anonymous> (bootstrap_node.js:*:*)
-    at emitNone (events.js:*:*)
     at Socket.emit (events.js:*:*)
     at endReadableNT (_stream_readable.js:*:*)
     at _combinedTickCallback (internal/process/next_tick.js:*:*)
+    at process._tickCallback (internal/process/next_tick.js:*:*)
 42
 42
 [stdin]:1
@@ -27,9 +27,9 @@ Error: hello
     at Module._compile (module.js:*:*)
     at evalScript (bootstrap_node.js:*:*)
     at Socket.<anonymous> (bootstrap_node.js:*:*)
-    at emitNone (events.js:*:*)
     at Socket.emit (events.js:*:*)
     at endReadableNT (_stream_readable.js:*:*)
+    at _combinedTickCallback (internal/process/next_tick.js:*:*)
 [stdin]:1
 throw new Error("hello")
 ^
@@ -42,9 +42,9 @@ Error: hello
     at Module._compile (module.js:*:*)
     at evalScript (bootstrap_node.js:*:*)
     at Socket.<anonymous> (bootstrap_node.js:*:*)
-    at emitNone (events.js:*:*)
     at Socket.emit (events.js:*:*)
     at endReadableNT (_stream_readable.js:*:*)
+    at _combinedTickCallback (internal/process/next_tick.js:*:*)
 100
 [stdin]:1
 var x = 100; y = x;
@@ -58,9 +58,9 @@ ReferenceError: y is not defined
     at Module._compile (module.js:*:*)
     at evalScript (bootstrap_node.js:*:*)
     at Socket.<anonymous> (bootstrap_node.js:*:*)
-    at emitNone (events.js:*:*)
     at Socket.emit (events.js:*:*)
     at endReadableNT (_stream_readable.js:*:*)
+    at _combinedTickCallback (internal/process/next_tick.js:*:*)
 
 [stdin]:1
 var ______________________________________________; throw 10