portfolio/rollup.config.js

import npm from 'rollup-plugin-node-resolve';

export default {
  entry: './src/js/d3.bundle.js',
  format: 'iife', //umd or iife
  moduleName: 'd3',
  plugins: [npm({jsnext: true})],
  dest: './assets/js/d3.bundle.js'
};