最近的Chrome / V8版本中的对象描述符getter / setter性能 [英] Object descriptor getter/setter performance in recent Chrome/V8 versions

问题描述

给定

  var obj = {}; 
 
 var _a = 1; 
 
 obj._a = 1; 
 
 obj.aGetter = function（）{
 return _a; 
} 
 
 obj.aSetter = function（val）{
 _a = val; 
 
 
 Object.defineProperty（obj，'a'，{
 enumerable：true，
 get：function（）{
 return _a; 
}，
 set：function（val）{
 _a = val; 
} 
}）; 
  

使用getter / setter函数

  obj.aSetter（2）; 
 obj.aGetter（）;与直接媒体访问相比，
  

的Chrome / V8性能有所下降（约3倍）：

  obj._a = 2; 
 obj._a; 
  

这是可以理解的。并使用描述符getter / setter

  obj.a = 2; 
 obj.a; 
  

会导致Chrome浏览器的性能降低30倍左右（41至最新）几乎和代理一样慢。虽然Firefox和旧版本的Chrome浏览器版本使用描述符getter / setter，但是性能不会有太大的损失。

最近Chrome / V8版本中描述符getter / setter性能的确切问题是什么？这是一个可以被监控的已知问题吗？

这些测量是使用Benchmark.js（jsPerf引擎）完成的。我无法提供jsPerf测试的链接来显示差异，因为jsPerf已经被其反DDoS措施严重搞砸了，但我确信现有的测试可以证明这一点。 p>

解决方案

性能变化与这个Chromium问题（积分转到@VyacheslavEgorov）。

为了避免性能问题，应该使用原型。这是类可能用于实例化对象一次的几个原因之一。

使用ES5：

  var _a = 1; 
 
函数Obj（）{} 
 
 Object.defineProperty（Obj.prototype，'a'，{
 enumerable：true，
 get：function （）{
 return _a; 
}，
 set：function（val）{
 _a = val; 
} 
}）; 
 
 var obj = new Obj（）; 
 //或
 var obj = Object.create（Obj.prototype）; 
  

或者使用ES6语法糖：

 class Obj {
 constructor（）{
 this._a = 1; 
} 
 
 get a（）{
 return this._; 
} 
 
 set a（val）{
 this._a = val; 
} 
} 
 
 let obj = new Obj（）; 
  

Given

var obj = {};

var _a = 1;

obj._a = 1;

obj.aGetter = function() {
  return _a;
}

obj.aSetter = function(val) {
  _a = val;
}

Object.defineProperty(obj, 'a', {
  enumerable: true,
  get: function () {
    return _a;  
  },
  set: function(val) {
    _a = val;
  }     
});

using getter/setter functions

obj.aSetter(2);
obj.aGetter();

will have some decrease in Chrome/V8 performance (~3x) when compared to direct property access:

obj._a = 2;
obj._a;

This is be understandable. And using descriptor getter/setter

obj.a = 2;
obj.a;

will cause ~30x decrease in Chrome (41 to latest) performance - almost as slow as Proxy. While Firefox and older Chrome versions use descriptor getter/setter with no significant performance penalty.

What is the exact problem with descriptor getter/setter performance in recent Chrome/V8 versions? Is it a known issue that can be monitored?

The measurements were done with Benchmark.js (jsPerf engine). I'm unable to provide a link to jsPerf test to visualize the difference because jsPerf has been seriously screwed up with its anti-DDoS measures, but I'm sure there are existing ones that can prove a point.

解决方案

The changes in performance are relevant to this Chromium issue (credits go to @VyacheslavEgorov).

To avoid performance issues, a prototype should be used instead. This is one of few reasons why classes may be used to instantiate an object once.

With ES5:

var _a = 1;

function Obj() {}

Object.defineProperty(Obj.prototype, 'a', {
  enumerable: true,
  get: function () {
    return _a;  
  },
  set: function(val) {
    _a = val;
  }     
});

var obj = new Obj();
// or
var obj = Object.create(Obj.prototype);

Or with ES6 syntactic sugar:

class Obj {
  constructor() {
    this._a = 1;
  }

  get a() {
    return this._a;
  }

  set a(val) {
    this._a = val;
  }     
}

let obj = new Obj();

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