Modern JavaScript build tools compile entire folder structures of JavaScript code into single, minified files that are near-impossible to read, but can also include source maps which can be used to display the original code in tools such as the Chrome DevTools Sources panel.
These source maps can be processed to extract mainly meaningful code and file structures, by installing a package calling Shuji and running a simple bash command.
Generally, production builds shouldn't include source maps, but if you do manage to lose your source files, or for some (obviously, ethical!) reason need to view the original files, and you happen to have / find the source maps, you're good to go.