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events: improve performance by ~120% #44627

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events: improve performance by ~120% #44627

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15 changes: 9 additions & 6 deletions lib/events.js
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Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,9 @@ const {
identicalSequenceRange,
} = require('internal/util/inspect');

function NullObject() {}
NullObject.prototype = ObjectCreate(null);

let spliceOne;

const {
Expand Down Expand Up @@ -338,7 +341,7 @@ EventEmitter.init = function(opts) {

if (this._events === undefined ||
this._events === ObjectGetPrototypeOf(this)._events) {
this._events = ObjectCreate(null);
this._events = new NullObject();
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@jasnell jasnell Oct 2, 2022

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This change is fairly problematic, I think. At the very least it's semver-major. Unfortunately we have a number of ecosystem modules that touch this._events directly and changing the type of thing that is can definitely break stuff.

this._eventsCount = 0;
}

Expand Down Expand Up @@ -547,7 +550,7 @@ function _addListener(target, type, listener, prepend) {

events = target._events;
if (events === undefined) {
events = target._events = ObjectCreate(null);
events = target._events = new NullObject();
target._eventsCount = 0;
} else {
// To avoid recursion in the case that type === "newListener"! Before
Expand Down Expand Up @@ -685,7 +688,7 @@ EventEmitter.prototype.removeListener =

if (list === listener || list.listener === listener) {
if (--this._eventsCount === 0)
this._events = ObjectCreate(null);
this._events = new NullObject();
else {
delete events[type];
if (events.removeListener)
Expand Down Expand Up @@ -740,11 +743,11 @@ EventEmitter.prototype.removeAllListeners =
// Not listening for removeListener, no need to emit
if (events.removeListener === undefined) {
if (arguments.length === 0) {
this._events = ObjectCreate(null);
this._events = new NullObject();
this._eventsCount = 0;
} else if (events[type] !== undefined) {
if (--this._eventsCount === 0)
this._events = ObjectCreate(null);
this._events = new NullObject();
else
delete events[type];
}
Expand All @@ -758,7 +761,7 @@ EventEmitter.prototype.removeAllListeners =
this.removeAllListeners(key);
}
this.removeAllListeners('removeListener');
this._events = ObjectCreate(null);
this._events = new NullObject();
this._eventsCount = 0;
return this;
}
Expand Down