alt Hacker NewsYes and no. Some patterns exist because the language isn't expressive enough. This is one reason why the patterns made sense in the OP's .NET programs, but made less sense in JS. JS simply doesn't require as much ceremony for some things because it's dynamically typed and reflection kind of comes for free.
I would say that reflection in JS is terrible compared to .NET. You can only just barely figure out what is in an object, but it's a hell of a time figuring out what any of those things can do. I wouldn't so much as call what JS does "reflection" any more than "making objects out of poorly implemented hashmaps."