Return string formatted utf16 expression from a character

utf16.js

function toUTF16(codePoint) {
    var TEN_BITS = parseInt('1111111111', 2);
    function u(codeUnit) {
      return '\\u'+codeUnit.toString(16).toUpperCase();
    }

    if (codePoint <= 0xFFFF) {
      return u(codePoint);
    }
    codePoint -= 0x10000;
    
    // Shift right to get to most significant 10 bits
    var leadSurrogate = 0xD800 + (codePoint >> 10);

    // Mask to get least significant 10 bits
    var tailSurrogate = 0xDC00 + (codePoint & TEN_BITS);

    return u(leadSurrogate) + u(tailSurrogate);
  }
  
//toUTF16('\xF6'.charCodeAt(0))   //  "\uF6"