JavaScript - Problem With Function Hoisting

javascript

JavaScript allows two ways of defining a function.  In the first method, called 
"function declaration", a new function is defined:

function foo() { ... }

This function has a name, foo.  Functions defined like this are hoisted.  
Regardless of where we define a function in the current scope, JavaScript would 
act as if the function was defined up front.  So:

foo(); // call the function before it is defined

function foo() { ... }

is perfectly valid.

The second way to define a function is by using a function expression.  In this 
case, provide a function definition in the context where JavaScript would 
expect to see an expression:

var foo = function foo() { ... }

Functions defined like this are not hoisted.  So:

foo(); // call the function before it is defined

var foo = function foo() { ... }

is not valid.

Functions defined as function expressions do not need to have names.  However, 
if we do provide a name, we won't be able to call the function by this name, 
but the function will use name when reporting errors.