Understanding pass by reference vs value with functions

Question

As I understand objects are passed by reference in JavaScript (and primitives are passed by value?).

var a, b;
a = {
    Foo: "Bar"
}
b = a;
a.Foo = "Other";
console.log(b.Foo); // "Other"

This worked similarly with arrays but did not work like I expect with functions:

var a, b;
a = function(){ return 20; }
b = a;
a = function(){ return 40; }
console.log(b()); // returns 20 ?

I'm confused because I thought functions are objects. Shouldn't the above example return 40?

Answer 1

In the first case, a.Foo = ..., You are changing the value of a property in the object, referred by both a and b. This is called mutating an object.

But in the second case, you are making a refer a new function object. Now, a and b are referring to different function objects.

That is why you are getting 20 in the second case.