Easy to be a senior frontend engineer. Just say you were already around when the current most hyped JS framework was released that everyone must move to, 1-2 years ago.
I think you confused the JS ecosystem with the C# one.
What do you mean?
Although I don't see why you're bashing C#. Despite the .NET Framework > .NET Core > .NET transitions, it's not really that different. There's a ton of new functionality and ways to do things, but for the most part the old ways still work too.