Question

I want to detect and block certain keyboard shortcuts on a web page. For example, say I want to prevent alt+tab for switching apps (just an example, assume any global shortcut).

Here’s as far as I can think it out:

• attach a keyboard event listener to
  document (or window?)
• use event.which to check which key
  combination was pressed
• if it was a blacklisted shortcut,
  stop the browser from executing it

But, I don’t know how to
A) detect multiple keys (e.g. alt and tab together), or
B) stop them from executing (can I just return false?).

Can anyone tell me how to accomplish the above?

Answer 1

You want to prevent screenshots from being taken? Forget it right now.

No matter what elaborate mechanisms you put into place, they will be trivial to circumvent by un-focusing the browser window (or just the document, e.g. by clicking into the address bar), and pressing the screenshot key then.

There is no chance for you to do this except by installing client software on the computer that controls what the user does, or maybe using some proprietary ActiveX control that makes its contents un-print-screenable. Both approaches are hugely difficult and have tons of downsides.