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

/*
character: 😂
codepoint 128514
hexadecimal 1f602
utf-8: F0 9F 98 82
utf-16: D8 3D DE 02
*/

console.log(xah_codepoint_to_utf16_hexStr(128514) === "D83D DE02");