I built websites and wrote JavaScript for a long time before discovering generics by returning to school and being forced to build data structures from scratch

I built websites and wrote JavaScript for a long time before discovering generics by returning to school and being forced to build data structures from scratch in java. Other than that, there's no way I'd have ever come across them. I was just turned down from a senior position because someone had more years of React experience, so we're not exactly in the most sophisticated hierarchy here. Seniority should probably not depend on your exposure to technical language mechanics, especially those that weren't related to your area of expertise.