For anyone who also wants to get the js object from dynamic query string of the url

mock.onGet(/api\/test\/?.*/).reply((config) => {
  console.log(config.url, parseQueryString(config.url));
  return [202, []];
});

function parseQueryString(url: string) {
  const queryString = url.replace(/.*\?/, '');

  if (queryString === url || !queryString) {
    return null;
  }

  const urlParams = new URLSearchParams(queryString);
  const result = {};

  urlParams.forEach((val, key) => {
    if (result.hasOwnProperty(key)) {
      result[key] = [result[key], val];
    } else {
      result[key] = val;
    }
  });

  return result;
}

Result

axios.get("api/test");
// api/test
// null

axios.get("api/test?foo=1&bar=two");
// api/test?foo=1&bar=two
// {foo: "1", bar: "two"}

axios.get("api/test?foo=FOO&bar=two&baz=100");
// api/test?foo=FOO&bar=two&baz=100
// {foo: "FOO", bar: "two", baz: "100"}

axios.get("api/test?foo=FOO&bar=two&foo=loo");
// api/test?foo=FOO&bar=two&foo=loo
// {foo: ["FOO", "loo"], bar: "two"}

Live Demo