基本上我要实现的是在中间件中检查上传的文件是否具有正确的图像类型（例如png）。到目前为止，这是我想出的：

export const fileCheckMiddleware = (req,res,next) => {
  const acceptedImageTypes = ["image/gif","image/jpeg","image/png"];

  const oldWrite = res.write;
  const oldEnd = res.end;

  const chunks = [];

  res.write = (...restArgs) => {
  chunks.push(new Buffer(restArgs[0]));
  oldWrite.apply(res,restArgs);
 };

  res.end = async (...restArgs) => {
if (restArgs[0]) {
  chunks.push(new Buffer(restArgs[0]));
}

const body = Buffer.concat(chunks).toString("utf8");

try {
  let parsedBody = {};
  try {
    parsedBody = JSON.parse(body);
  } catch (err) {
    parsedBody = { data: { unparsedBody: body } };
  }

  const { variables } = req.body;

  console.log("\x1b[1m%s\x1b[0m","LOG variables",variables.file);
  if (variables.file) {
    console.log("\x1b[1m%s\x1b[0m","LOG type",typeof variables.file);
  }
} catch (err) {}
oldEnd.apply(res,restArgs);
   };
  next();
};

记录的变量类型。文件是一个对象。而console.log的结果是这样的：

LOG variables Promise {
 { filename: 'trump.jpeg',mimetype: 'image/jpeg',encoding: '7bit',createReadStream: [Function: createReadStream] } }

那么我如何在这里访问模仿类型？我试图映射键，variables.file [“ Promise”]，...