Prepros comes with built in support for UglifyJS.
Prepros 6.0.16 had a bug that prevented Prepros from uglifying/minifying files. It's been fixed in the latest version but old projects must be configured manually to disable beautify. Please go to `Project Settings` -> `Other` -> `Uglify` then disable `Beautify` option.
Project Settings ->
Uglify to change uglify settings.