Answer 1

const urls = [
  "https://www.xx.cn/api?keyword=&level1=&local_batch_id=&elective=&local_province_id=33",
  "https://www.xx.cn/api?keyword=&level1=&local_batch_id=&elective=800&local_province_id=33",
  "https://www.xx.cn/api?keyword=&level1=&local_batch_id=&elective=800,700&local_province_id=33",
];

function getElective(url) {
  const reg = new RegExp("(^|&)elective=([^&]*)(&|$)", "i");
  const r = url.substr(1).match(reg);

  if (r != null) {
    return r[2] ? r[2].split(",") : [];
  }

  return [];
}

urls.forEach((url) => {
  const result = getElective(url);
  console.log(result, "---result");
});