function codeBlockName(unicode) {
  if (unicode > 0x2FA1F) {
    if (unicode >= 0xE0000 && unicode <= 0xE007F) return 'Tags';
    if (unicode >= 0xE0100 && unicode <= 0xE01EF) return 'Variation Selectors Supplement';
    if (unicode >= 0xF0000 && unicode <= 0xFFFFF) return 'Supplementary Private Use Area-A';
    if (unicode >= 0x100000 && unicode <= 0x10FFFF) return 'Supplementary Private Use Area-B';
    return undefined;
  }
  const candidates = codeRangeIndex[Math.floor(unicode/0x100)];
  if (candidates === undefined) return undefined;
  for (const name in candidates) {
    const [ lower, upper ] = candidates[name];
    if (unicode >= lower && unicode <= upper) return name;
  }
  return undefined;
}
Code range name of a unicode, return undefined if the corresponding range 
is undefined
@param { number } unicode Character code in number 
@returns { string | undefined }