build-url: the good way

build-url.js

function buildUrl(url, options) {
  const baseUrl = _getBaseUrl(url);
  const opts = _getOptions(url, options);

  if (!opts) {
    return baseUrl;
  }

  urlWithPath = _appendPath(baseUrl, opts.path);
  urlWithPathAndQueryParams = _appendQueryParams(urlWithPath, opts.queryParams)
  urlWithPathQueryParamsAndHash = _appendHash(urlWithPathAndQueryParams, opts.hash);

  return urlWithPathQueryParamsAndHash;
};

function _getBaseUrl(url) {
  if (url === null || typeof(url) === 'object') {
    return '';
  }
  return url;
}

function _getOptions(url, options) {
  if (typeof(url) === 'object') {
    return url;
  }
  return options;
}

function _appendPath(baseUrl, path) {
  if (!path) {
    return baseUrl;
  }
  return baseUrl += '/' + path;
}

function _appendQueryParams(urlWithPath, queryParams) {
  if (!queryParams) {
    return urlWithPath
  }

  const keyValueStrings = Object.keys(queryParams).map(key => {
    return `${key}=${queryParams[key]}`;
  });
  const joinedKeyValueStrings = keyValueStrings.join('&');

  return `${urlWithPath}?${joinedKeyValueStrings}`;
}

function _appendHash(urlWithPathAndQueryParams, hash) {
  if (!hash) {
    return urlWithPathAndQueryParams;
  }
  return `${urlWithPathAndQueryParams}#${hash}`;
}

Refactored version of main file from build-url module: https://github.com/steverydz/build-url/blob/master/src/build-url.js