How to detect whether a browser supports window.close?

Question

I'm building an app, where the auth flow goes as follows

• user clicks login button
• a login window opens.
• The user is redirected to either Facebook, Google or Twitter, depending on the querystring of the window.
• When the user comes back from fb/google/twitter, my backend generates an auth token, and the popup window uses postMessage to send the auth token to the main page, verifying the origin
• the main page closes th window after receiving the token.

This flow works great on desktop devices, but not in mobile browsers, where window.open opens a new tab that can't be programmatically closed.

On mobile devices, I can redirect the user to the login screen, and send them back with the auth token in the hash fragment (oauth2 implicit flow), but I only want to do that when I have to. How do I detect whether window.close works without browser sniffing?

What I've tried

I've tried using a HTML/JS based modal dialog with an iframe in it, but Google's login page doesn't allow embedding it in an iFrame, I haven't tried with other providers

Answer 1

You can check if window.close() is supported by object detection:

if (window.close) {
    alert ('window close is supported');
}

Do the check without paranthesis (), as you don't want to execute the function, but want to check for existance of the function/object.