Cleaning

By default, tsdown removes stale files from the output directory (outDir). Files that the build emits again are overwritten in place. Files left over from a previous build, and nothing else that the new build produced, are deleted only after the new output is on disk.

Watch mode uses the same rule on every successful rebuild. A tool that reads outDir while tsdown --watch is running (Vite, Nest, tsc --watch) keeps seeing the previous files until each one is replaced. The directory is not emptied first.

Builds that share an output directory, including the ESM and CJS formats of one package, are cleaned together. Each format keeps the files it just emitted. Only files that none of them emitted again are removed, and only after the last of those builds has finished.

Disable cleaning entirely with --no-clean:

tsdown --no-clean

NOTE

clean: true still deletes every file under the clean target that this build did not emit. Do not point it at a directory that contains files you need to keep.