What's the purpose of referencing the window object in Javascript?

Question

Every property of the window object is a global variable. This means you can do something like this:

window.foo = 42;
alert(foo); //alerts 42
var bar = 3;
alert(window["bar"]); //alerts 3

Because of this, I've always wondered what the purpose was of referencing window in code like this

if(window.prompt("Enter Password") === "secret") {
  window.location.hash = "authorized";
  window.open("secretPage.html");
}

when you could omit window and have code that does exactly the same thing:

if(prompt("Enter Password") === "secret") {
  location.hash = "authorized";
  open("secretPage.html");
}

The use also seems inconsistent; I almost never see window.alert but I'll frequently see window.location.

Do people just like referencing window to make their code more verbose? Is there some good reason for doing this that I don't know about?

Answer 1

One situation in which it helps to be explicit is that it will be immediately clear inside a function that you intend to modify a global variable. For example:

function blah() {
    // a bunch of code preceding...
    test = "aha!";
}

Did someone forget to declare test with var? Or is this intentional modification of a global? Compare:

function blah() {
    // a bunch of code preceding...
    window.test = "aha!";
}

Now it's immediately clear what is intended. Of course, you know, globals should be avoided in the first place, but you get my point.

Answer 2

window is implicit, but it's good code practice to avoid ambiguity where possible.