编写 getter 作为原型

Question

我正在努力对我的 javascript 代码进行性能更新。

在 Firefox 中我收到了这个警告：

mutating the [[Prototype]] of an object will cause your code to run very slowly; instead create the object with the correct initial [[Prototype]] value using Object.create

我写了一些脚本来证明这一点，结果非常好：没有突变的简单脚本运行速度提高了 66%。

但是我在转换我的代码时遇到了问题，我不会写 getters:

这是我现在拥有的：

// Class
function FooBar(options) {
  this.options = options;
}

// Prototype
FooBar.prototype = {

  // Getters
  get a() {
      return this.options.a;
    },

    get b() {
      return this.options.b;
    },

    get ab() {
      return this.options.a + this.options.b;
    },

    // Methods
    displayOptions: function() {
      console.log(this.options);
    }
};

// Code
var options = {
  a: 'foo',
  b: 'bar'
};

var fooBar = new FooBar(options);

console.log(fooBar.a);
console.log(fooBar.b);
console.log(fooBar.ab);
fooBar.displayOptions();

在 return 中使用 this 关键字作为原型的 getter 是问题所在。

如果我使用 Object.defineProperty this 关键字是错误的，除非我在构造函数中这样做，但它会在 class 的每个实例上重新创建属性并减慢我的速度代码进一步下降。

Answer 1

这行得通（我只是在之前的尝试中弄乱了语法）：

// Class
function FooBar (options) {
 this.options = options;
}

//Prototype getters
Object.defineProperty(FooBar.prototype, 'a', {
 get: function() {
  return this.options.a;
 }
});

Object.defineProperty(FooBar.prototype, 'b', {
 get: function() {
  return this.options.b;
 }
});


Object.defineProperty(FooBar.prototype, 'ab', {
 get: function() {
  return this.options.a + this.options.b;
 }
});

// Methods
FooBar.prototype.displayOptions = function() {
 console.log(this.options);
};

// Code
var options = {
 a:'foo',
 b:'bar'
};

var fooBar = new FooBar (options);

console.log(fooBar.a);
console.log(fooBar.b);
console.log(fooBar.ab);
fooBar.displayOptions();

对于那些对将这样的脚本更快地转换为运行的好处感到好奇的人：运行以下代码并查看控制台中的输出 (Chrome - 66%更快，Firefox - 没什么区别（很好奇，因为我收到了来自 Firefox 的警告））：

// WITHOUT PROTOTYPING
var Person1 = function() {
 this.name = 'myName';
 this.changeName = function(name) {
  this.name = name;
 };
 this.changeName2 = function(name) {
  this.name = name;
 };
 this.changeName3 = function(name) {
  this.name = name;
 };
 this.changeName4 = function(name) {
  this.name = name;
 };
}


// WITH PROTOTYPING, WITH MUTATION
var Person2 = function() {
 this.name = 'myName';
}
Person2.prototype = {
 changeName: function(name) {
  this.name = name;
 },
 changeName2: function(name) {
  this.name = name;
 },
 changeName3: function(name) {
  this.name = name;
 },
 changeName4: function(name) {
  this.name = name;
 }
};

// WITH PROTOTYPING, WITHOUT MUTATION
var Person3 = function() {
 this.name = 'myName';
}
Person3.prototype.changeName = function(name) {
 this.name = name;
};
Person3.prototype.changeName2 = function(name) {
 this.name = name;
};
Person3.prototype.changeName3 = function(name) {
 this.name = name;
};
Person3.prototype.changeName4 = function(name) {
 this.name = name;
};


// DO THE TEST
var i=0, len=1000000;

// TEST1
window.performance.mark('mark_test_start');
for(i=0;i<len;i++) {
 p = new Person1();
 p.changeName('myName2');
}
window.performance.mark('mark_test_end');
window.performance.measure('no-prototyping', 'mark_test_start', 'mark_test_end');


// TEST2
window.performance.mark('mark_test2_start');
for(i=0;i<len;i++) {
 p = new Person2();
 p.changeName('myName2');
}
window.performance.mark('mark_test2_end');
window.performance.measure('prototyping-with-mutation', 'mark_test2_start', 'mark_test2_end');

// TEST3
window.performance.mark('mark_test3_start');
for(i=0;i<len;i++) {
 p = new Person2();
 p.changeName('myName2');
}
window.performance.mark('mark_test3_end');
window.performance.measure('prototyping-without-mutation', 'mark_test3_start', 'mark_test3_end');



// OUTPUT tests
var items = window.performance.getEntriesByType('measure');
for (var i = 0; i < items.length; ++i) {
  var req = items[i];
  console.log(req.name + ': ' + req.duration.toFixed(2));
}

编写 getter 作为原型

Write getters as a prototype

javascript

getter

setter

prototype

mutation