Javascript: 'window' is not defined

Question

I'm trying to learn JavaScript, but the following code has been giving me a lot of trouble:

window.onload = function () {
    for ( var i = 0; i < seats.length; i++) {
        for ( var j = 0; j < seats.length; j++) {
            document.getElementById(getSeatId(i, j)).onclick = function(evt) {
                getSeatStatus(getSeatId(i, j));
            };
        }
    }
    document.getElementById("search").onclick = findSeat;
    document.getElementById("male_search").onclick = findMaleSeats;
    initSeats();
};

It is from an external JS file and it is the only file linked to the page. findSeat, findMaleSeats, getSeatId, and initSeats are all defined a little bit later in the file. When I double click this file, I get the following error:

Windows Script Host
Error: 'window' is not defined
Code: 800A1391

I already tried moving the code to other places in the file, assigning a different function (even an empty function) to window.onload and many other things. It just seems that my computer doesn't know what window is. And if I try to open the HTML in a browser the nothing loads (as one would expect).

Does someone know what is wrong with this?

Answer 1

Trying to access an undefined variable will throw you a ReferenceError.

A solution to this is to use typeof:

if (typeof window === "undefined") {
  console.log("Oops, `window` is not defined")
}

or a try catch:

try { window } catch (err) {
  console.log("Oops, `window` is not defined")
}

While typeof window is probably the cleanest of the two, the try catch can still be useful in some cases.

Answer 2

It is from an external js file and it is the only file linked to the page.

OK.

When I double click this file I get the following error

Sounds like you're double-clicking/running a .js file, which will attempt to run the script outside the browser, like a command line script. And that would explain this error:

Windows Script Host Error: 'window' is not defined Code: 800A1391

... not an error you'll see in a browser. And of course, the browser is what supplies the window object.

ADDENDUM: As a course of action, I'd suggest opening the relevant HTML file and taking a peek at the console. If you don't see anything there, it's likely your window.onload definition is simply being hit after the browser fires the window.onload event.