The reason some of the variables are blocked is because that would allow the app to do other stuff than is intended. Otherwise you can change document.location and redirect to a malware site.
I just looked up ES6 and I think this is what code.org is missing.
From what I understand, @infinitestasis is correct.
To provide some more context, App Lab’s primary purpose is a learning tool to support the Computer Science Principles curriculum. Its capabilities definitely go beyond that, but some of the limitations are under that lens (and I’m sure, as mentioned by @infinitestasis, some limitations are for security).
Thus we understand (and forewarn ) that using functions/commands that aren’t in the App Lab toolbox may not be supported.
I’m wondering if there’s some substitute commands we can use for what you’re trying to do. println sounds very much like console.log. Not sure about the alerts though, as I don’t think App Lab supports popping up a new window. The closest might be to just display a label on the screen, or switch to a new screen with the message and an “ok” button.