encodeURIComponent()

// Encodes characters such as ?,=,/,&,:
console.log(`?x=${encodeURIComponent("test?")}`);
// 予想される結果: "?x=test%3F"
console.log(`?x=${encodeURIComponent("шеллы")}`);
// 予想される結果: "?x=%D1%88%D0%B5%D0%BB%D0%BB%D1%8B"

encodeURIComponent(uriComponent)

const fileName = "my file(2).txt";
const header = `Content-Disposition: attachment; filename*=UTF-8''${encodeRFC5987ValueChars(
  fileName,
)}`;
console.log(header);
// "Content-Disposition: attachment; filename*=UTF-8''my%20file%282%29.txt"
function encodeRFC5987ValueChars(str) {
  return (
    encodeURIComponent(str)
      // The following creates the sequences %27 %28 %29 %2A (Note that
      // the valid encoding of "*" is %2A, which necessitates calling
      // toUpperCase() to properly encode). Although RFC3986 reserves "!",
      // RFC5987 does not, so we do not need to escape it.
      .replace(
        /['()*]/g,
        (c) => `%${c.charCodeAt(0).toString(16).toUpperCase()}`,
      )
      // The following are not required for percent-encoding per RFC5987,
      // so we can allow for a little better readability over the wire: |`^
      .replace(/%(7C|60|5E)/g, (str, hex) =>
        String.fromCharCode(parseInt(hex, 16)),
      )
  );
}

function encodeRFC3986URIComponent(str) {
  return encodeURIComponent(str).replace(
    /[!'()*]/g,
    (c) => `%${c.charCodeAt(0).toString(16).toUpperCase()}`,
  );
}

// 上位・下位の正しいペア
encodeURIComponent("\uD800\uDFFF"); // "%F0%90%8F%BF"
// 上位のみであり "URIError: malformed URI sequence" が発生
encodeURIComponent("\uD800");
// 下位のみであり "URIError: malformed URI sequence" が発生
encodeURIComponent("\uDFFF");