How do programmers know what code to write before starting to work?

In "How do programmers know what code to write before starting to work?" I answer a programming question.

[recycle-bin-camp]

"how many time it will take you to fix the problem you didn't make on the project you never seen and where packages are outdated for 3 years?"

[shibnathroy]

"With a bad word in front of person" 😂 🤣

[Fm]

Hey Frederic, I have a request. Would it be possible to show us how the SOLID principles can be applied to a react application? I think I get the principles but I am struggling with implementation.