Webpack 4 - build / watch optimization & configuration

I have a WordPress theme that used Webpack and I recently upgraded it to use Webpack 4. When I run "npm run watch", my dev server starts, and my assets get rebuilt. This is correct. My issue is when I then save one of my ".scss" files, all of the assets (js / images/ fonts /scss) all get rebuilt again together. That is not what I want. I'm looking for when I save my ".scss" files, it then only recompiles those, not everything else. Same with my js/ images /fonts. (if I had a new image, images should run again, not the whole thing, if I save a JS file, js should run again, not the whole thing, etc) The "CSS" also needs to be injected, instead of reloading the page. I also have this set in "browser sync" but that doesn't seem to be working anymore. If this sounds like something you can update inside my config using Webpack 4+ please let me know.