shift-jisのURLにaxiosでpostする

const axios = require('axios');
const Encoding = require('encoding-japanese');

function toSJIS(keyword) {
  const unicodeArray = Array.from(keyword, char => char.charCodeAt(0));
  const sjisArray = Encoding.convert(unicodeArray, { to: 'SJIS', from: 'UNICODE' });
  return Encoding.urlEncode(sjisArray);
};

async function test() {
    const keyword = 'あああ';
    const sjisKeyword = toSJIS(keyword);
    const data = `param1=${sjisKeyword}&param2=2`;
    const response = await axios.post('https://example.com/xxxxx', data, {
      headers: {
        'Content-Type': 'application/x-www-form-urlencoded; charset=shift_jis'
      },
      responseType: 'arraybuffer',
      transformResponse: data => new TextDecoder('shift-jis').decode(data)
    });
    console.log(response);
}
test();