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Window

window.self & WindowProxy​

  • window.self === window
  • self is just a reference to the global window object in browsers.
  • WindowProxy is an internal mechanism that makes things like iframes and cross-origin windows appear like windows, while actually handling some safety and redirection under the hood.

So what's self?

In the browser:

console.log(self === window); // true

It's literally just another name for window. People often use self inside web workers (where there's no window), but in the main thread, it's basically the same as window.

So this:

if (window.self === window.top) {
  console.log('This window is not in an iframe.');
}

...is a way to check if you're not inside an iframe.

Then what the heck is WindowProxy?

That's where things get weird and internal.

When you access window.frames[0] or window.open(...), you get back an object that looks like a window, but it's actually a WindowProxy.
A WindowProxy is like a magic wrapper that forwards your calls to the actual Window object - but only if you're allowed to.

Why?

  • It helps enforce cross-origin security.
  • If you try to access properties on a window from another domain, the proxy can block you.
  • If the frame navigates to another page (even the same origin), the proxy stays the same, but the underlying Window object changes.

The idea is: the thing you have a reference to is stable (WindowProxy), even though what's behind it might change (Window).

Bottom line

You almost never have to worry about WindowProxy directly unless you're doing iframe or cross-origin work. If you're just wondering what self is — it's a simple alias for window. Nothing fancy. Just the beginning of a deep dive 😄

window.open()​

The open() method of the Window interface loads a specified resource into a new or existing browsing context (that is, a tab, a window, or an iframe) under a specified name.

Syntax​

open()
open(url)
open(url, target)
open(url, target, windowFeatures)

window.parent​

The Window.parent property is a reference to the parent of the current window or subframe.

If a window does not have a parent, its parent property is a reference to itself.

When a window is loaded in an <iframe>, <object>, or <frame>, its parent is the window with the element embedding the window.

window.top​

Returns a reference to the topmost window in the window hierarchy.

window.isSecureContext​

window.isSecureContext returns true when the page is being served in a secure context, which usually means:

  • The page is served over HTTPS
  • Or it's running on localhost (which is treated as secure)