Is passing the window object to an IIFE optional?

Question

Is there any difference between the following examples?

example 1:

(function (window) {
 'use strict';
  console.log(window)
})(window);

example 2:

(function () {
 'use strict';
  console.log(window)
})();

Is passing the window object optional?

Answer 1

There's not much point to #1. window is read-only and cannot be redefined, so there's no need to capture its value at a point in time the way #1 does. #2 is fine.

The pattern #1 uses is primarily useful for capturing things that may get changed by other code later, e.g.:

var x = 1;
(function(x) {
    setTimeout(function() {
        console.log("inside, x = " + x);
    }, 100);
})(x);
x = 2;
console.log("outside, x = " + x);

...or to get convenient shorthand names for things:

(function(d) {
    var div = d.createElement("div");
    div.innerHTML = "Hi";
    d.body.appendChild(div);
})(document);

It was also commonly used for getting undefined in case the undefined identifer was modified:

(function(u) {
    console.log(typeof u); // "undefined"
})(/*Note there's no argument passed*/);

Now that undefined is read-only and cannot be redefined, there's no real need to do that anymore.