From d5fb78982a82285a7abe76c4bd4bb888e8f616c1 Mon Sep 17 00:00:00 2001
From: Anatoli Papirovski <apapirovski@mac.com>
Date: Sun, 15 Oct 2017 00:44:47 -0400
Subject: events: use spread function param in emit

With recent changes in V8, it is now as performant or faster to use
spread parameter within EventEmitter.prototype.emit, especially
in cases where looping over arguments is required.

events/ee-emit.js n=2000000               4.40 %    *** 1.505543e-06
events/ee-emit-1-arg.js n=2000000         2.16 %    *** 2.434584e-10
events/ee-emit-2-args.js n=2000000        1.05 %     ** 0.001764852
events/ee-emit-3-args.js n=2000000        2.18 %    *** 3.234954e-08
events/ee-emit-6-args.js n=2000000       17.17 %    *** 1.298702e-103
events/ee-emit-10-args.js n=2000000      17.14 %    *** 1.144958e-97

This has a knock-on effect for modules that use events extensively,
such as http2:

http2/headers.js nheaders=0 n=1000        2.10 %    *** 6.792106e-11

PR-URL: https://github.com/nodejs/node/pull/16212
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
---
 lib/events.js | 40 +++++++++++++++++-----------------------
 1 file changed, 17 insertions(+), 23 deletions(-)

(limited to 'lib/events.js')

diff --git a/lib/events.js b/lib/events.js
index bd6a368661..79a722674c 100644
--- a/lib/events.js
+++ b/lib/events.js
@@ -162,23 +162,22 @@ function emitMany(handler, isFn, self, args) {
   }
 }
 
-EventEmitter.prototype.emit = function emit(type) {
-  var er, handler, len, args, i, events, domain;
-  var needDomainExit = false;
-  var doError = (type === 'error');
+EventEmitter.prototype.emit = function emit(type, ...args) {
+  let doError = (type === 'error');
 
-  events = this._events;
+  const events = this._events;
   if (events !== undefined)
     doError = (doError && events.error === undefined);
   else if (!doError)
     return false;
 
-  domain = this.domain;
+  const domain = this.domain;
 
   // If there is no 'error' event listener then throw.
   if (doError) {
-    if (arguments.length > 1)
-      er = arguments[1];
+    let er;
+    if (args.length > 0)
+      er = args[0];
     if (domain !== null && domain !== undefined) {
       if (!er) {
         const errors = lazyErrors();
@@ -202,37 +201,32 @@ EventEmitter.prototype.emit = function emit(type) {
     return false;
   }
 
-  handler = events[type];
+  const handler = events[type];
 
   if (handler === undefined)
     return false;
 
+  let needDomainExit = false;
   if (domain !== null && domain !== undefined && this !== process) {
     domain.enter();
     needDomainExit = true;
   }
 
-  var isFn = typeof handler === 'function';
-  len = arguments.length;
-  switch (len) {
-    // fast cases
-    case 1:
+  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:
-      emitOne(handler, isFn, this, arguments[1]);
+      emitTwo(handler, isFn, this, args[0], args[1]);
       break;
     case 3:
-      emitTwo(handler, isFn, this, arguments[1], arguments[2]);
-      break;
-    case 4:
-      emitThree(handler, isFn, this, arguments[1], arguments[2], arguments[3]);
+      emitThree(handler, isFn, this, args[0], args[1], args[2]);
       break;
-    // slower
     default:
-      args = new Array(len - 1);
-      for (i = 1; i < len; i++)
-        args[i - 1] = arguments[i];
       emitMany(handler, isFn, this, args);
   }
 
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