Multer中间件有问题，我创建了中间件，并将静态Express文件设置到Uploads文件夹中。
Index.js文件

import emailroutes from './routes/emailroutes.js'

app.use(express.json({ limit: '25mb' }));
app.use(express.urlencoded({ extended: false, limit: '25mb' }));
app.use('/uploads', express.static(path.join('uploads')));
app.use('/email', emailroutes);

然后在routes文件中，使用multer作为中间件

import EmailController from '../controller/EmailController.js'
import { storageMultiple } from '../helpers/storage.js'
router.post('/', protect, storageMultiple, EmailController.postEmail)

Multer中间件功能如下。

import multer from 'multer';
import md5 from 'md5';
var filepatharray = [];

const diskStorageMultiple = multer.diskStorage({
    destination: (req, file, cb) => {
        cb(null, 'uploads');
    },
    filename: (req, file, cb) => {
        while (i < req.files.length) {
            filepath = md5(Date.now() + i)
            const mimeType = file.mimetype.split('/');
            var fileType = mimeType[1];
            if (fileType == 'vnd.openxmlformats-officedocument.spreadsheetml.sheet') {
                fileType = 'xlsx'
            } else if (fileType == 'text/plain') {
                fileType = 'txt'
            } else if (fileType == 'text/csv') {
                fileType = 'csv'
            } else if (fileType == 'vnd.ms-excel') {
                fileType = 'xls'
            } else if (fileType == 'vnd.openxmlformats-officedocument.wordprocessingml.document') {
                fileType = 'docx'
            } else if (fileType == 'msword') {
                fileType = 'doc'
            } else if (fileType == 'vnd.openxmlformats-officedocument.presentationml.presentation') {
                fileType = 'pptx'
            } else if (fileType == 'vnd.ms-powerpoint') {
                fileType = 'ppt'
            }
            const fileName = filepath + '.' + fileType;
            filepatharray.push({
                path: filepath + '.' + fileType,
                name: file.originalname
            })

            cb(null, fileName);
            i++;
        }
    },
});
const fileFilter = (req, file, cb) => {
    cb(null, true)
};

const storageMultiple = multer({
    storage: diskStorageMultiple,
    fileFilter: fileFilter).array(
    'files'
);

export { storageMultiple , filepatharray}

当我改变这个单一的文件上传，它的工作很好，以下是为单一文件multer的代码。

const diskStorage = multer.diskStorage({
    destination: (req, file, cb) => {
        cb(null, './uploads');
    },
    filename: (req, file, cb) => {
        filepath = md5(Date.now() + req.user.id)
        const mimeType = file.mimetype.split('/');
        var fileType = mimeType[1];
        if (fileType == 'vnd.openxmlformats-officedocument.spreadsheetml.sheet') {
            fileType = 'xlsx'
        } else if (fileType == 'text/plain') {
            fileType = 'txt'
        } else if (fileType == 'text/csv') {
            fileType = 'csv'
        } else if (fileType == 'vnd.ms-excel') {
            fileType = 'xls'
        } else if (fileType == 'vnd.openxmlformats-officedocument.wordprocessingml.document') {
            fileType = 'docx'
        } else if (fileType == 'msword') {
            fileType = 'doc'
        } else if (fileType == 'vnd.openxmlformats-officedocument.presentationml.presentation') {
            fileType = 'pptx'
        } else if (fileType == 'vnd.ms-powerpoint') {
            fileType = 'ppt'
        }
        const fileName = filepath + '.' + fileType;
        filepath = filepath + '.' + fileType
        cb(null, fileName);
    },
});
const storage = multer({ storage: diskStorage, fileFilter: fileFilter }).single(
    'file'
);

当我使用多个文件时，我将在multer中作为“文件”发送，而当使用单个文件时，则是“文件”
我期待着，如果有人帮助调试哪里是服务器上的问题。