Output Preserve Modules

Instead of creating as few chunks as possible, this mode will create separate chunks for all modules using the original module names as file names. Tree-shaking will still be applied, suppressing files that are not used by the provided entry points or do not have side effects when executed and removing unused exports of files that are not entry points. On the other hand, if plugins emit additional "virtual" files to achieve certain results, those files will be emitted as actual files using a pattern ${output.virtualDirname}/fileName.js.

It is therefore not recommended to blindly use this option to transform an entire file structure to another format if you directly want to import from those files as expected exports may be missing. In that case, you should rather designate all files explicitly as entry points by adding them to the input option object. See the glob pattern example for how to do this dynamically.