sitebuilder-wrapper.js

// Helper Functions
const wrapWith = wrapper => obj => key => val => wrapper({...obj, [key]: val});
const wrapWithSiteBuilder = wrapWith(SiteBuilder);

// Expression Builder
function SiteBuilder(value) {
  const siteBuilderWrapper = wrapWithSiteBuilder(value);
  return {
    withSiteName: siteBuilderWrapper('name'),
    withDomain: siteBuilderWrapper('domain'),
    build: () => value
  };
}

SiteBuilder({}).withSiteName('hello').withDomain('some-domain').build();