Object Oriented Programming
Regardless of the programming language, the concepts of object oriented programming remain the same. This is why I invested a lot of time mastering these concepts to gurantee excellence in delivery.
Source Control
In other words, teamwork. I personally believe that source control is one of the core skills to have in today's digital world. I'm proficient in utilizing Git in my work regardless of the scope because documentation saves the day.
UI/UX
What is the use of code if we overlook the delivery? I believe that frontend design is as important as backend design, this is why I invest a lot of my time learning about different UI/UX technologies.
Research
As a developer, research is a core skill. Whether it was researching to fix a bug on Stackoverflow or researching with actual users to validate a design and test it, this skill always comes in handy.