Thanks for explanations, Sreenath Somarajapuram.
I think it will be fine to leave some options to developers to say keep node_components and bower_components, and also, it gonna be very important to make sure all untracked files generated by build process will be removed after run "mvn clean". For example, we cannot add node_component and bower_components gitignore file from all branches. That causes issue if a developer switch to a different branch.
I would like to propose one solution: can we cleanup npm_components, etc. by default, and have an option (like -Dkeep-yarn-ui-build-files) to explicitly tell mvn to keep these temporary files. Sounds like a plan? Sunil G.
For npm-cached: does it store files in a default location such as ~/.npm? Just like maven, we will store downloaded files to local ~/.m2, this cannot solve all the issues, but can speed up the whole build since it doesn't need to re-download dependencies.
For unit test, not quite sure when the issues will be triggered. What does the "cache proxy" means? Is the "cache proxy" enabled by default? And what efforts needed for enable hinting?