什么是JavaScript中的函数Empty()? [英] What is - function Empty() - in javascript ?

问题描述

我具有此功能:

函数fff(){}

哪个是 function ，它是 Function构造函数

所以 fff .__ proto __ 应该告诉我: function Function(){[native code]}

但事实并非如此.

它显示: functionEmpty(){}

我只能在 __ proto __ 的 constructor 属性中看到 function Function(){[native code]}

It is only at the constructor property of __proto__ that I see function Function() { [native code] }

问题:

这是什么 functionEmpty(){} function
以及为什么 fff .__ proto __ 不会显示给我: function Function(){[native code]} ?

What is this function Empty() {} function
and why fff.__proto__ won't show me : function Function() { [native code] } ?

nb我知道 __ proto __ 是查找链中用于解析方法等的实际对象. prototype 是用于构建的对象>使用 new 创建对象时 __ proto __ .

nb I know that __proto__ is the actual object that is used in the lookup chain to resolve methods, etc. prototype is the object that is used to build __proto__ when you create an object with new.

但是再说一次:函数 fff 是通过更新 Function构造函数在后台实例化的函数. ...如此吗?

But again : function fff is a function which is instantiated behind the scenes by newing Function constructor....so ?

推荐答案

您误会了 __ proto __ .

__ proto __ 返回对象继承的原型值；不是其构造函数.

__proto__ returns the prototype value that the object inherits; not its constructor.

所有函数(包括 Function 本身)都继承 Function.prototype .
因此， Function .__ proto__ === Function.prototype 为true.
在规范的 15.3.4 部分中指定了此对象:

All functions (including Function itself) inherit Function.prototype.
Thus, Function.__proto__ === Function.prototype is true.
This object is specified in section 15.3.4 of the spec:

Function原型对象本身就是一个Function对象(其 [[Class]] 是"Function" )，该对象在被调用时将接受任何参数并返回未定义的

The Function prototype object is itself a Function object (its [[Class]] is "Function") that, when invoked, accepts any arguments and returns undefined.

另请参见

15.3.4.2 Function.prototype.toString()

返回函数的依赖实现的表示形式.此表示形式具有 FunctionDeclaration 的语法.特别要注意的是，在String表示中空格，行终止符和分号的使用和放置取决于实现.

15.3.4.2 Function.prototype.toString ( )

An implementation-dependent representation of the function is returned. This representation has the syntax of a FunctionDeclaration. Note in particular that the use and placement of white space, line terminators, and semicolons within the representation String is implementation-dependent.

toString 函数不是通用的；如果此值不是Function对象，则抛出TypeError异常.因此，不能将其传递给其他类型的对象用作方法.

The toString function is not generic; it throws a TypeError exception if its this value is not a Function object. Therefore, it cannot be transferred to other kinds of objects for use as a method.

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