Programming LanguagesJavaScript
Learnt this in free time as a teen, but I improved here while working on projects involving NodeJS and web frameworks
TypeScript
Learnt for a better sense of safety about Javascript code I developed,.
Also its very powerful typesystem helped protect against potential bugs and is often self-documenting.
I've used this heavily in a handful of linked-together (private) NPM React/generic libraries.
C#
Learnt in free-time, and covered in Level 3 Software-Development Apprenticeship. See ASP .NET Core for previous project discussion.