Create one bundle per script with Rollup

rollup.config.js

const FS = require('fs');
const Path = require('path');

const paths = {
  src: 'src',
  build: 'build'
};

const files = FS.readdirSync(paths.src)
  .map((name) => Path.resolve(paths.src, name))
  .map((path) => Object.assign({path}, Path.parse(path)))
  .filter(({ext}) => ext === '.js');

export default files.map(({path, name, base}) => ({
  input: path,
  output: {
    file: Path.join('build', base),
    format: 'umd',
    name
  }
}));