Returns the number of bytes the given Javascript string takes if encoded as a UTF16 byte array, EXCLUDING the null terminator byte.
function lengthBytesUTF32(str) {
  var len = 0;
  for (var i = 0; i < str.length; ++i) {
    // Gotcha: charCodeAt returns a 16-bit word that is a UTF-16 encoded code unit, not a Unicode code point of the character! We must decode the string to UTF-32 to the heap.
    // See http://unicode.org/faq/utf_bom.html#utf16-3
    var codeUnit = str.charCodeAt(i);
    if (codeUnit >= 0xD800 && codeUnit <= 0xDFFF) ++i; // possibly a lead surrogate, so skip over the tail surrogate.
    len += 4;
  }

  return len;
}