Options object merged with defaults in ES2015+

optionDefaults.js

function createSite(name, assignedOptions = {}) {
  const defaultOptions = {
    html: 'jade',
    styles: 'scss',
    scripts: 'babel',
    whitespace: '2 spaces',
  };
  const options = Object.assign({}, defaultOptions, assignedOptions);

  /*
   * In the future you will be able to use the spread operator instead of Object.assign().
   * It is currently at stage 2 of ECMAScript drafts.
   * https://github.com/sebmarkbage/ecmascript-rest-spread
  */

  // const options = {
  //   ...defaultOptions,
  //   ...assignedOptions,
  // };
};