This might get downvoted and all but ... I'm not sure how someone who has written C# for 8 years would think this.
I'm not even talking complicated things. Just OO basics like interfaces and abstract classes (with compile time enforcement) are pretty helpful as you evolve a code base.
IMO:
In the lower level architecture it's just more powerful designing functions and data structures to play with each other as you wish (but power is not necessarily a good thing, you can shoot yourself in the foot). You just do it, no need to define all those fancy interfaces, abstract methods, base classes...
In the higher level architecture, sure, you really miss those securities that interfaces and such enforces, JavaScript is amazingly breakable. But, fortunately, JavaScript/Node community modularizes so often (and well), that this is practically not an issue. The modules are well done, tested, there's community input, etc.
Or what if I want to check if a property exists in a dynamic object? Catch the exception? Use the ExpandoObject? Will this affect performance?
What about local delegates?
And I just won't start with reflection. Have you seem those snippets on SO? Now compare the same with JavaScript.
Don't get me wrong, I've been developing in C# for some good years in a row and I really like the language. C# traditional OO way of doing things kinda gets you by the hand when design your application. JavaScript is more on your shoulders. It's a tradeoff, you have to be more careful but you also have more power.
What about local delegates? Func<int, int> localDelegate = x => x + 1;
You don't need to use reflection as often in c# as you would in javascript.
I can't imagine trying to do such a thing in JS, which provides so little information about exactly what I'm reflecting over. And it's so clunky. Some things you can typeof, some you have to instanceOf, such that you basically end up doing both all the time.
With JS, I know that I have a bag full of things named something. I have to do my own work from there to find out if they are methods or properties or fields. In C#, I can just ask it to give me all of the properties. Oh, but stick to just the public ones. Or skip any that have an attribute named "Exclude" tagged to them.
Yeah, I have no idea what people are talking about that JS is better for reflection. That's just bonkers.
Also, the way the various Microsoft frameworks use strings to specify property and type names drives me insane. It's just like.. "Hey, we have a really nice type and generics system... but here lets hop around that and instead use strings that we hope you never need to refactor, as well as magic method names (ie, RegisterRoutes, Application_Start)". This seems to be getting a little better, but it's still way too prevalent. It's almost like the people responsible for writing C# frameworks had a disagreement over strict typing and decided to just contaminate a ton of APIs to spite the type system.