That breaks the web by definition. There is no way to implement a non-blocking alert(), confirm(), or prompt() in a way that doesn't break existing code that uses them, and that's a lot of code, a lot of the web.
the alert(), confirm(), and prompt() themselves interrupt normal browsing, so I'm not sure what you mean here. They're synchronous so block the main thread, but they also block other user interactions until they're dismissed, so what would be the benefit in leaving normal browsing unaffected if the user cannot browse anyway?
