function getBaseUrl(url) {
  const regex = /^(https?:\/\/[^\/?#]+)(?:[\/?#]|$)/i;
  const match = url.match(regex);
  return match && match[1];
}

// 示例
console.log(getBaseUrl('https://www.example.com/path/to/page?query=string#fragment'));
// 输出: "https://www.example.com"

function getBaseUrlWithPort(url) {
  const regex = /^(https?:\/\/[^\/?#:]+(?::\d+)?)(?:[\/?#]|$)/i;
  const match = url.match(regex);
  return match && match[1];
}

// 示例
console.log(getBaseUrlWithPort('http://localhost:8080/path'));
// 输出: "http://localhost:8080"

function getFullBaseUrl(url) {
  const regex = /^(https?:\/\/[\w\-\.]+(?:\.\w{2,})?(?::\d+)?)(?:[\/?#]|$)/i;
  const match = url.match(regex);
  return match && match[1];
}

// 示例
console.log(getFullBaseUrl('https://sub.domain.co.uk:3000/path'));
// 输出: "https://sub.domain.co.uk:3000"

// 使用URL API的替代方案
function getBaseUrlUsingURLAPI(url) {
  try {
    const urlObj = new URL(url);
    return `${urlObj.protocol}//${urlObj.host}`;
  } catch (e) {
    return null;
  }
}

// 预编译正则表达式
const baseUrlRegex = /^(https?:\/\/[^\/?#]+)(?:[\/?#]|$)/i;

function getBaseUrlOptimized(url) {
  const match = baseUrlRegex.exec(url);
  return match && match[1];
}

function getBaseUrlFromRelative(relativeUrl, base) {
  try {
    const absoluteUrl = new URL(relativeUrl, base).href;
    return getBaseUrlUsingURLAPI(absoluteUrl);
  } catch (e) {
    return null;
  }
}