rollup.config.mjs

// Plugins
import terser from '@rollup/plugin-terser';
import { readFileSync } from "fs";
const pkg = JSON.parse(readFileSync('package.json', {encoding: 'utf8'}));
// import pkg from './package.json';

// Configs
var configs = {
  name: 'blog',
  files: ['menu-toggle.js','prism.js','styleswitcher.js'],
  formats: ['es'],
  default: 'es',
  pathIn: 'source/_assets/js',
  pathOut: 'source/assets/js',
  minify: true,
  sourceMap: false
};

// Banner
// var banner = `/*! ${configs.name ? configs.name : pkg.name} v${pkg.version} | (c) ${new Date().getFullYear()} ${pkg.author.name} | ${pkg.license} License | ${pkg.repository.url} */`;
var banner = ``;

var createOutput = function (filename, minify) {
  return configs.formats.map(function (format) {
    var output = {
      file: `${configs.pathOut}/${filename}${format === configs.default ? '' : `.${format}`}${minify ? '.min' : ''}.js`,
      format: format,
      banner: banner
    };
    if (format === 'iife') {
      output.name = configs.name ? configs.name : pkg.name;
    }
    if (minify) {
      output.plugins = [terser()];
    }

    output.sourcemap = configs.sourceMap

    return output;
  });
};

/**
 * Create output formats
 * @param  {String} filename The filename
 * @return {Array}           The outputs array
 */
var createOutputs = function (filename) {

  // Create base outputs
  var outputs = createOutput(filename);

  // If not minifying, return outputs
  if (!configs.minify) return outputs;

  // Otherwise, ceate second set of outputs
  var outputsMin = createOutput(filename, true);

  // Merge and return the two arrays
  return outputs.concat(outputsMin);

};

/**
 * Create export object
 * @return {Array} The export object
 */
var createExport = function (file) {
  return configs.files.map(function (file) {
    var filename = file.replace('.js', '');
    return {
      input: `${configs.pathIn}/${file}`,
      output: createOutputs(filename)
    };
  });
};

export default createExport();