unicode string encoder/decoder for ascii

mini-uni-golf.js

const toHexCharCode = char => char.charCodeAt(0).toString(16).padStart(2, '0');
function encodeGolf(plain) {
  return unescape( // enter unicode escape codes land
    plain.match(/[\s\S]{1,2}/g) // split string into pairs of letters
      .map(([a, b]) => b ? '%uD8' + toHexCharCode(a) + '%uDC' + toHexCharCode(b) : a) // encode each pair as a high surrogate and low surrogate in unicode (where an odd character, just include it unencoded to preserve odd length)
      .join('') // concatenate the escape codes as a string
  ); // exit escape codes land; return actual unicode characters
}

// 5 bytes fewer than decode
function decodeGolf(encoded) {
  return unescape( // enter unicode escape codes land
    escape(encoded) // convert the input into escape codes
      .replace(/u../g, '') // strip the first two code digits (marker for high/low surrogate) to encode the implanted ascii character
  ); // exit escape codes land; return the plaintext
}
// minified
const decodeGolf_minifiedSource = encodedSource => `unescape(escape\`${encodedSource}\`.replace(/u../g,''))`;

function golfSource(source) {
  const encodedSource = encodeGolf(source);
  const autoRunningEncodedSource = `eval(${decodeGolf_minifiedSource(encodedSource)})`;
  return autoRunningEncodedSource;
}

mini-uni.js

const toHexCharCode = char => char.charCodeAt(0).toString(16).padStart(2, '0');
function encode(plain) {
  return unescape( // enter unicode escape codes land
    plain.match(/[\s\S]{1,2}/g) // split string into pairs of letters
      .map(([a, b]) => b ? '%u' + toHexCharCode(a) + toHexCharCode(b) : a) // encode each pair as a unicode escape code (where an odd character, just include it unencoded to preserve odd length)
      .join('') // concatenate the escape codes as a string
  ); // exit escape codes land; return actual unicode characters
}

function decode(encoded) {
  return unescape( // enter unicode escape codes land
    escape(encoded) // convert the input into escape codes
      .replace(/u(..)/g, '$1%') // map each first two code digits to a separate code to encode an ascii character
  ); // exit escape codes land; return the plaintext
}

also see https://xem.github.io/codegolf/obfuscatweet.html