当一个函数什么都不返回时，为什么返回值不为空？

Question

Why the value of x is undefined in case 1; Why doesnt it also be null like case 2? My understanding is that , in case 1, since f has no return value, so x is pointing to null (no return value)

Case 1

f = () => {return}

x = f()

console.log(x) // -->undefined

------------------

f = () => {return null}

x = f()

console.log(x) // -->null

Answer 1

Because the specification says so :

A return statement causes a function to cease execution and, in most cases, returns a value to the caller. If Expression is omitted, the return value is undefined . Otherwise, the return value is the value of Expression .

Answer 2

据我所知，当某些东西没有被传递时，函数必然会返回一些东西，默认情况下它是undefined的，就像如果你在没有任何参数的情况下记录它会记录未定义一样。

console.log() // undefined

Answer 3

Basically, when you define a variable without assigning a value, It will become undefine.

When you assign a "Null" value, the value of the variable become null (you are indeed assigning a value)

In your case, you dont return a value(not assigning any value), you get a undefine

Answer 4

Hope this makes it clearer for you