Difference of two ways to "create" a function.

gistfile1.js

// example 1
(function () {
  console.log(typeof func); // 'function'
  function func () {}
  console.log(typeof func); // 'function'
})();


// example 2
(function () {
  console.log(typeof func); // 'undefined'
  var func = function () {};
  console.log(typeof func); // 'function'
})();

// For each variable declaration,
// a property with a same name but value `undefined` 
// is added to the **variable object** of **execution context** (the former is a property of the latter),
// when entering a **execution context** (but before the code execution).


// example 3
(function () {
  console.log(typeof func); // 'undefined'
  (function func () {});
  console.log(typeof func); // 'undefined'
})();

// Function object created by function-expression does not affect **variable object**,
// because it is not a declaration, will not be parsed on entering a **execution context**,
// but on code execution.
// In this example, **variable object** has no property named `func`.
// So, if such function object is not assigned to a variable or a property of an object,
// it will be only called on the spot or recursively,
// after that, you can not access it (even it has a name since function-expression does not affect **variable object**),
// and garbage collection will release its memory.