JS: Char to UTF-16 Encoding 📜

Here is a function that return the hexadecimal string of UTF-16 Encoding of a unicode character's codepoint.

/*
xah_codepoint_to_utf16_hexStr(zcodepoint) return a string of hexadecimal that's the UTF-16 encoding of the char of codepoint zcodepoint (integer).
The result string is not padded, but one space is inserted to separate the first 2 bytes and last 2 bytes. Digits are in CAPITAL case.

URL http://xahlee.info/js/js_utf-16_encoding.html
Version: 2022-10-17 2025-12-22
*/
const xah_codepoint_to_utf16_hexStr = (zcodepoint) => {
 const xCharStr = String.fromCodePoint(zcodepoint);
 if (zcodepoint < 2 ** 16) {
  return xCharStr.charCodeAt(0).toString(16).toUpperCase();
 } else {
  const xLen = String.fromCodePoint(zcodepoint).length;
  const xout = [];
  for (let i = 0; i < xLen; i++) {
   xout.push(xCharStr.charCodeAt(i).toString(16).toUpperCase());
  }
  return xout.join(" ");
 }
};

// s------------------------------
// test

console.assert(xah_codepoint_to_utf16_hexStr(129419) === "D83E DD8B");

/*
🦋
BUTTERFLY
ID 129419
HEXD 1F98B
UTF8  F0 9F A6 8B
UTF16 D83E DD8B
*/