function isIdentifierStart(code, astral) {
  if (code < 65) return code === 36;
  if (code < 91) return true;
  if (code < 97) return code === 95;
  if (code < 123) return true;
  if (code <= 0xffff)
    return (
      code >= 0xaa && nonASCIIidentifierStart.test(String.fromCharCode(code))
    );
  if (astral === false) return false;
  return isInAstralSet(code, astralIdentifierStartCodes);
}
@param {number} code
@param {boolean} astral