.babelrc

{
  "presets": [
    [
      "es2015",
      {
        "modules": false
      }
    ]
  ],
  "plugins": [
    "external-helpers"
  ]
}

bundle.js

/******/ (function(modules) { // webpackBootstrap
/******/ 	// The module cache
/******/ 	var installedModules = {};
/******/
/******/ 	// The require function
/******/ 	function __webpack_require__(moduleId) {
/******/
/******/ 		// Check if module is in cache
/******/ 		if(installedModules[moduleId]) {
/******/ 			return installedModules[moduleId].exports;
/******/ 		}
/******/ 		// Create a new module (and put it into the cache)
/******/ 		var module = installedModules[moduleId] = {
/******/ 			i: moduleId,
/******/ 			l: false,
/******/ 			exports: {}
/******/ 		};
/******/
/******/ 		// Execute the module function
/******/ 		modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);
/******/
/******/ 		// Flag the module as loaded
/******/ 		module.l = true;
/******/
/******/ 		// Return the exports of the module
/******/ 		return module.exports;
/******/ 	}
/******/
/******/
/******/ 	// expose the modules object (__webpack_modules__)
/******/ 	__webpack_require__.m = modules;
/******/
/******/ 	// expose the module cache
/******/ 	__webpack_require__.c = installedModules;
/******/
/******/ 	// identity function for calling harmony imports with the correct context
/******/ 	__webpack_require__.i = function(value) { return value; };
/******/
/******/ 	// define getter function for harmony exports
/******/ 	__webpack_require__.d = function(exports, name, getter) {
/******/ 		if(!__webpack_require__.o(exports, name)) {
/******/ 			Object.defineProperty(exports, name, {
/******/ 				configurable: false,
/******/ 				enumerable: true,
/******/ 				get: getter
/******/ 			});
/******/ 		}
/******/ 	};
/******/
/******/ 	// getDefaultExport function for compatibility with non-harmony modules
/******/ 	__webpack_require__.n = function(module) {
/******/ 		var getter = module && module.__esModule ?
/******/ 			function getDefault() { return module['default']; } :
/******/ 			function getModuleExports() { return module; };
/******/ 		__webpack_require__.d(getter, 'a', getter);
/******/ 		return getter;
/******/ 	};
/******/
/******/ 	// Object.prototype.hasOwnProperty.call
/******/ 	__webpack_require__.o = function(object, property) { return Object.prototype.hasOwnProperty.call(object, property); };
/******/
/******/ 	// __webpack_public_path__
/******/ 	__webpack_require__.p = "";
/******/
/******/ 	// Load entry module and return exports
/******/ 	return __webpack_require__(__webpack_require__.s = 0);
/******/ })
/************************************************************************/
/******/ ([
/* 0 */
/***/ (function(module, exports) {

/** @license MIT License (c) copyright 2010-2016 original author or authors */

  // Non-mutating array operations

  // cons :: a -> [a] -> [a]
  // a with x prepended
  function cons (x, a) {
    var l = a.length;
    var b = new Array(l + 1);
    b[0] = x;
    for (var i = 0; i < l; ++i) {
      b[i + 1] = a[i];
    }
    return b
  }

  // append :: a -> [a] -> [a]
  // a with x appended
  function append (x, a) {
    var l = a.length;
    var b = new Array(l + 1);
    for (var i = 0; i < l; ++i) {
      b[i] = a[i];
    }

    b[l] = x;
    return b
  }

console.log(append(5, [1, 2, 3, 4]));
console.log(cons(1, [2, 3, 4]));


/***/ })
/******/ ]);

index.js

import { append, cons } from '@most/prelude'

console.log(append(5, [1,2,3,4]))
console.log(cons(1, [2,3,4]))

webpack.config.js

const path = require('path')
const rollupBabel = require('rollup-plugin-babel')

module.exports = {
  entry: './index.js',
  output: {
    filename: 'bundle.js',
    path: path.resolve(__dirname, 'dist')
  },
  module: {
    rules: [
      {
        exclude: /(node_modules)/,
        test: /\.js$/,
        use: {
          loader: 'webpack-rollup-loader',
          options: {
            plugins: [
              rollupBabel({
                exclude: 'node_modules/**'
              })
            ]
          }
        }
      }
    ]
  }
}