v4 and back to es5

uglify-es is not supported anymore so we returned back to old school uglify-js. If you still want to transpile es6+ try rollup-plugin-terser. Terser is actively developed fork of uglify-es with the new name.

In this version we changed the way to import plugin. Now it looks like this

import { uglify } from 'rollup-plugin-uglify';

export default {
  ...
  plugins: [uglify()]
  ...
}

To see more prettier errors uglify shows also babel code frame

    > 1 | var = 1
        |    ^ Name expected

Error: Error transforming bundle with 'uglify' plugin: Name expected