I buy your argument about frameworks providing structure. And most software projects are a untestable spaghetti mess, it's not because of vanilla JS though, spaghetti code have been written in many different languages. The problem is inexperienced engeneers, and old design patterns in school books, like Classes ;)
I've been designing software for over 15 years and here's some tips that works well for JS and probably other languages too:
1) Avoid code couplings, if you keep couplings at a minimal, you only have to test the code once and it will never break.
2) Modular code: All dependencies should be contained! Dependencies should be branched, not entangled/complexed
3) Independent functions: Functions should not have any dependencies from the outside scope, not even other functions if possible. Use lexical modules and sub-functions.
4) Event listeners: Have independent "micro services" that listen for events instead of orchestrating.
5) Abstractions: Make it possible to use functions/modules without knowledge about the abstracted code.
6) Avoid state =)
I've been designing software for over 15 years and here's some tips that works well for JS and probably other languages too:
1) Avoid code couplings, if you keep couplings at a minimal, you only have to test the code once and it will never break. 2) Modular code: All dependencies should be contained! Dependencies should be branched, not entangled/complexed 3) Independent functions: Functions should not have any dependencies from the outside scope, not even other functions if possible. Use lexical modules and sub-functions. 4) Event listeners: Have independent "micro services" that listen for events instead of orchestrating. 5) Abstractions: Make it possible to use functions/modules without knowledge about the abstracted code. 6) Avoid state =)