javascript - 原型(prototype)链无法检索 Function.prototype 中的属性集

Question

当我将属性添加到 Function.prototype 时，为什么它会从链中消失？为什么属性 yyy(在属性链中)未定义？

function Shape() { }
Shape.prototype.xxx = 111;
Function.prototype.yyy = 222;

let x = new Shape;

console.log(x.xxx) // 111
console.log(x.yyy) // undefined???

Answer 1

Function.prototype 只在 functions 的原型(prototype)链上，所以它不在你的 x 对象的原型(prototype)链上，因为不是函数。 (是的，这有点令人困惑。)

函数X 的prototype 属性用于设置通过new X 或Object 创建的对象的原型(prototype)。创建(X)。

您的Shape.prototype 的原型(prototype)是Object.prototype，而不是Function.prototype。 (Function.prototype 是函数 Shape 的原型(prototype)。)

您的代码创建了两个原型(prototype)链，一个用于函数 Shape，一个用于 Shape.prototype(和 x):

+−−−−−−−−−−−−−−−+        +−−−−−−−−−−−−−−−−−−−−+| Shape         |   +−−−>| Function.prototype | +−−−−−−−−−−−−−−−|   |    +−−−−−−−−−−−−−−−−−−−−+ | [[Prototype]] |−−−+    | [[Prototype]]      |−−−+| prototype     |−−−+    | yyy: 222           |   |+−−−−−−−−−−−−−−−+   |    +−−−−−−−−−−−−−−−−−−−−+   |                    |                              \    +−−−−−−−−−−−−−−−−−−−−+                     \   +−−−−−−−−−−−−−−−−−−−−+     +−−>|  Object.prototype  |                      +−>| Shape.prototype    |    /    +−−−−−−−−−−−−−−−−−−−−+                     /   +−−−−−−−−−−−−−−−−−−−−+   |                    |    | [[Prototype]]      |−−−+                    |    | xxx: 111           |                    |    +−−−−−−−−−−−−−−−−−−−−++−−−−−−−−−−−−−−−+   ||       x       |   |+−−−−−−−−−−−−−−−+   || [[Prototype]] |−−−++−−−−−−−−−−−−−−−+

As you can see, since Function.prototype isn't in x's chain, x.yyy is undefined. But Shape.yyy is, since Shape inherits from Function.prototype:

function Shape() { }
Shape.prototype.xxx = 111;
Function.prototype.yyy = 222;

let x = new Shape;

console.log(x.xxx);     // 111
console.log(x.yyy);     // undefined
console.log(Shape.yyy); // 222