有没有办法以编程方式确定 function 实际上是 Javascript 中的 object？

Question

In Javascript, functions are objects. Yet typeof of a function returns function instead of object for ECMAScript compatibility reasons .

Is this function type actually some kind of wrapper for object that can be determined somehow? Or in Javascript, is a function actually fundamentally different from object s?

I do understand that functions are effectively and practically objects. But are they by definition actually completely separate from Objects in Javascript, or is there a way to programmatically reveal the Object that the Function is made of?

Answer 1

As the spec says :

an object is a member of the built-in type Object; and a function is a callable object

So

Or in Javascript, is a function actually fundamentally different from objects?

Not really, except for the fact that a function is callable - more precisely, that it has a [[Call]] internal method.

Functions inherit from objects in a very similar way that objects inherit from objects. For example, for a given function:

function foo(){}
foo.a = 'a';

There is:

• The foo function, which is an object, and has a [[Call]] internal method, as well as an a property, and a few other properties that functions have (like name )
• The foo function inherits from Function.prototype
• Function.prototype inherits from Object.prototype
• Object.prototype inherits from nothing - that's the start of the prototype chain

is there a way to programmatically reveal the Object that the Function is made of?

That's not really how it is - the function itself is an object. If the function object has properties, it'll be visible directly on the function. For example, above, referencing foo.a will give you the string 'a' . The a property isn't separate from the function - it's directly on the function object.