It removes comments and licences

[alvarotrigo]

Right not it seems to remove all comments with their licenses.
It would be nice to have something like gulp-uglify does. preserveComments: 'license'

[caiguanhao]

No. This plugin uses the free version of Javascript Obfuscator. It doesn't have the feature you mentioned. However, it has a feature called "Keep Header Comment" in the advanced version.