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() {
      return {
        post(endpoint, data) {
          return executor({
            url: `${baseUrl}${endpoint}`,
            data,
            method: 'POST',
            headers,
          });
        },
        get(endpoint, params) {
          return executor({
            url: `${baseUrl}${endpoint}`,
            params,
            method: 'GET',
            headers,
          });
        },
      };
    }
    return { forBaseUrl };
  })();
}