SystemJS package an existing bundle

build.js

var Builder = require("systemjs-builder");

var builder = new Builder({
  baseURL: "node_modules",
  map: {
    "jquery": "jquery/dist/jquery.js",
    "text": "systemjs-plugin-text/text.js",
    "css": "systemjs-plugin-css/css.js",
    "clerk": "."
  },
  paths: {
    "clerk/*": "./*"
  },
  packages: {
    "clerk": {
      "main": "module"
    },
    "mu-jquery-app": {
      main: "dist/mu-jquery-app.js"
    }
  },
  meta: {
    "mu-jquery-widget/widget": {
      build: false
    }
  }
});

builder
  .bundle('mu-jquery-app + clerk', 'outfile.js')
  .then(function () {
    console.log('Build complete');
  })
  .catch(function (err) {
    console.log('Build error');
    console.log(err);
  });

module.js

var widget = require("mu-jquery-widget/widget");

module.exports = widget.extends({
  "test": 123
});

package.json

{
  "name": "build",
  "version": "0.0.0",
  "description": "",
  "main": "",
  "author": "",
  "license": "",
  "devDependencies": {
    "jquery": "^3.2.1",
    "systemjs-builder": "^0.16.4"
  },
  "dependencies": {
    "mu-jquery-app": "^20.0.0"
  }
}