Cannot overwrite function from inside the function [duplicate]

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.