I agree it is totally non-obvious to developers without exposure to other programming environments. But that’s part of what you need to learn, the same way you learn to free() memory in C, delete objects in C++, use with keyword in Python, invoke the close method of objects that have one in Java…
As Javascript emerges from being a quick-and-dirty webpage gimmick to being a solid development platform, javascript developers too will have to learn correct programming idioms eventually.
Maybe the documentation should insist more on this. I believe there should be a section about integrating external code and common caveats.
But, yes, it would be possible to make the check a warning indeed.
Actually, I believe only the debug version of ember does this check. If you load ember.prod.js instead, all asserts should be gone, including this one. On the other hand, if you load ember.debug.js (the default version), it seems to be reasonable that such mistakes trigger failed assertions. After all, in debugging mode, you’re trying to pinpoint code issues.