client.js

function executeWithFetch(request) {
  // EXERCISE FOR THE READER
}

function executeWithAxios(request) {
  // EXERCISE FOR THE READER
}

function ClientBuilder() {
  return (function () {
    let baseUrl, headers, executor;
    function forBaseUrl(_baseUrl) {
      baseUrl = _baseUrl;
      return { withHeaders };
    }
    function withHeaders(_headers) {
      headers = _headers;
      return { usingFetch, usingAxios };
    }
    function usingFetch() {
      executor = executeWithFetch;
      return { build };
    }
    function usingAxios() {
      executor = executeWithAxios;
      return { build };
    }
    function build() {
      function post(endpoint, data) {
        return executor({
          url: `${baseUrl}${endpoint}`,
          data,
          method: 'POST',
          headers,
        });
      }
      function get(endpoint, params) {
        return executor({
          url: `${baseUrl}${endpoint}`,
          params,
          method: 'GET',
          headers,
        });
      }
      return { post, get };
    }
    return { forBaseUrl };
  })();
}