To be honest I had a quick look at your node, but it is not clear to me how it works. Have been investigating a lot of nodes in the last years, and they all have a rather similar setup. But not the one you have forked. A bit too confusing for me after a heavy day at work ...
Yes that is executed when you open the edit panel of your node, so in the flow editor (client).
It has an endpoint, so it is server side...
If you want to start debugging your client side nodes, you can easily get started via the chrome debugger (see my tutorial here). For your client side code, you can start the developer tools when the flow editor is open (after you have added a debugger statement e.g. to your oneditprepare function...).
From your code from yesterday:
life360.circles(session)
.then(...
circles is a promise and not an array, so it has no length.
If I were you I would read a book about Javascript, and start developing/forking a less complex node. And then continue with this node. Otherwise this will become a very long discussion ...
