In current Outlook version (Desktop), when opening our Outlook Web add-in, we can use "Inspect" option (by performing right click from the mouse) in the web add-in taskpane (right side pan) as...
As a side note, I've done all of my development against outlook.office.com because it's much easier to debug. The smart alerts run in the same context as the outlook application, so you can easily set breakpoints on it.