undefined is the same as undefined?

undefined.js

// 1) simple check
console.log(undefined === undefined); // true

// 2) check undefined param in function
(function (undef) {
  console.log(undef === undefined); // true
}());

// 3) unexists property
(function (obj) {
  console.log(obj.x === undefined); // true
}({}));

// 4) not set value for variable
(function () {
  var x;
  console.log(x === undefined); // true
}());

// 5) not exists item in array
(function (arr) {
  console.log(arr[1] === undefined); // true
})([5]);

// 6) define variable with 'undefined' with only create var
(function () {
  var a = undefined;
  var b;
  console.log(a === b); // true
}());