Multer中有两个函数：
对于要上载单个文件，请用途：

upload.single('avatar')

对于要上载多个文件，请用途：

upload.array('photos', 12) //here 12 is max number of files to upload.

请参考以下示例代码：

const express = require("express");
const multer = require("multer");
const app = express();
const multerStorage = multer.memoryStorage();
// Filter files with multer if you need
const multerFilter = (req, file, cb) => {
if (file.mimetype.startsWith("image")) {
cb(null, true);
} else {
cb("upload only images.", false);
}
};
const upload = multer({
storage: multerStorage,
fileFilter: multerFilter,
});
app.post('/singleUpload', upload.single('avatar'), function (req, res,
next) {
// req.body will hold the text fields, if there were any
console.log(req.file);//req.file is the `avatar` file. here avatar is
input field name
})
app.post('/multipleUpload', upload.array('photos', 12), function (req,
res, next) {
// req.body will contain the text fields, if there were any
// req.files is array of `photos` files.here avatar is
input field name
console.log(req.files);
})

希望这对你有帮助。