It is possible to use both languages, but you need to place them in specific folders within your project, then the way they compile means that they only work one way i.e. C# gets compiled before JS, JS can see C# but C# cannot see JS. Read this link, especially Point 3 :
However, it would be more prudent of you to convert the scripts and use just one language, eg choose C# or uJS for your project. Then you will never have the problem of one language not being able to see the other. Also if you convert the scripts, you will actually learn how to read both uJS and C# !
Here’s some links I found useful in converting between C# and uJS :