Cannot overwrite function from inside the function [duplicate]

Question

I got an unexpected result. Here's the code:

b = function c() {
  console.log(c);
  c = 3;
  console.log(c);
}
b();

I thought the second console.log should print "3" but instead I got the function itself. Why?

---

Meanwhile, from the code below I got the right "3".

function ff() {
  ff = 3;
  console.log(ff);
}
ff();

Answer 1

You are using a function expression:

FunctionExpression :
function Identifier_opt ( FormalParameterList_opt ) { FunctionBody }

So b = function c() { ... }; is perfectly valid, strict mode or otherwise. What happens to c is another question. According to the specs:

The production
FunctionExpression : function Identifier ( FormalParameterList_opt ) { FunctionBody }
is evaluated as follows:

[...]
3. Call the CreateImmutableBinding concrete method of envRec passing the String value of Identifier as the argument.
4. Let closure be the result of creating a new Function object as specified in 13.2 [...]
5. Call the InitializeImmutableBinding concrete method of envRec passing the String value of Identifier and closure as the arguments.
[...]

NOTE
The Identifier in a FunctionExpression can be referenced from inside the FunctionExpression's FunctionBody to allow the function to call itself recursively. However, unlike in a FunctionDeclaration, the Identifier in a FunctionExpression cannot be referenced from and does not affect the scope enclosing the FunctionExpression.

So:

• c is visible inside the function but not outside it
• c cannot be overwritten from inside the function (an "immutable" binding)

Meanwhile, from the code below I got the right "3".
function ff() {

This is a function declaration; different (and more obvious) rules apply here.

Answer 2

You cannot overwrite the function's named variable inside its own declaration. NFE (Named Function Expression) name cannot be overwritten (because it is constant)

This is clear when you write in strict JS mode. Try the example below:

'use strict';

var b = function c(){
  console.log(c);
  c = 3; // c still is a function
  console.log(c);
}

b();