URLSearchParams: URLSearchParams() コンストラクター

new URLSearchParams()
new URLSearchParams(options)

// url.search からパラメーターを取得し、コンストラクターに渡す
const url = new URL("https://example.com?foo=1&bar=2");
const params1 = new URLSearchParams(url.search);
// URL オブジェクトから直接 URLSearchParams オブジェクトを取得する
const params1a = url.searchParams;
// 文字列リテラルを渡す
const params2 = new URLSearchParams("foo=1&bar=2");
const params2a = new URLSearchParams("?foo=1&bar=2");
// ペアの列を渡す
const params3 = new URLSearchParams([
  ["foo", "1"],
  ["bar", "2"],
]);
// レコードを渡す
const params4 = new URLSearchParams({ foo: "1", bar: "2" });

const url = new URL("https://example.com/?a=hello&b=world");
console.log(url.href);
// https://example.com/?a=hello&b=world
console.log(url.origin);
// https://example.com
const add_params = {
  c: "a",
  d: new String(2),
  e: false.toString(),
};
const new_params = new URLSearchParams([
  ...Array.from(url.searchParams.entries()), // [["a","hello"],["b","world"]]
  ...Object.entries(add_params), // [["c","a"],["d","2"],["e","false"]]
]).toString();
console.log(new_params);
// a=hello&b=world&c=a&d=2&e=false
const new_url = new URL(`${url.origin}${url.pathname}?${new_params}`);
console.log(new_url.href);
// https://example.com/?a=hello&b=world&c=a&d=2&e=false
// (URL, Record<string, string>) を受け取る関数の形式で
const addSearchParams = (url, params = {}) =>
  new URL(
    `${url.origin}${url.pathname}?${new URLSearchParams([
      ...Array.from(url.searchParams.entries()),
      ...Object.entries(params),
    ])}`,
  );