packages/react-scripts/config/env.js
function fsExistsSync(path) {
  try {
    fs.accessSync(path, fs.F_OK);
  } catch (e) {
    return false;
  }
  return true;
}
function fsExistsSync(path) {
  try {
    fs.accessSync(path, fs.F_OK);
  } catch (e) {
    return false;
  }
  return true;
}
判断pages文件夹是否存在