Looking to Mimic GMail page change detection behavior

I would like to have my web app be abple to pop open new windows like GMail does 开发者_C百科for chats and phone calls but I'd also like to be able to detect if they click on something in the nav that will take the main window to another URL and break the code running in the popups windows.

Ideally it would prompt them and give them a chance to cancel the page change and not break the app. Any ideas how GMail does this?

You want to use the onbeforeunload event. The string you return will be displayed to the user in a dialog, giving the user the option of canceling the page navigation.