every .js code makes error in compilation

I have most source code in c# but I use some from external asset sources included into project that are .js , but when I try to compile them it gives me an error(All C# are ok and alco cooperation between scripts is ok, this problem persists even if there is empty .js file). I illustrate this situation on this screen:

To be honest I have read similar questions and solutions and I feel stupid, but I did not understand how to fix this problem at all. (I suspect it does somethink to do with linkage of sources but I am not sure or yet miss experience how to manage it) Only way I figured out to make it work was the tip from someone to delete in references everything except unityEngine.dll , but I have to do this when I start MonoDevelop editor all the time.

Can someone please give me advice how to fix this definitely?