Multer upload is not a function

// Multer upload config
const fs = require('fs');
const path = require('path');
const multer = require('multer');
const storage = multer.diskStorage({
    destination: function (req, file, cb) {
        cb(null, '/tmp/')
    },
    filename: function (req, file, cb) {
        const uniqueSuffix = Date.now() + '-' + Math.round(Math.random() * 1E9)
        cb(null, file.fieldname + '-' + uniqueSuffix + path.extname(file.originalname))
    }
})
const upload = multer({storage: storage});
app.post('/uploadPhoto', (req, res, next) => {
    upload.single('filename_here')(req, res, function (err) {
        if (err) {
            // A Multer error occurred when uploading.
            res.json({msg: err.message})
        } else {
            // Everything went fine.
            // req.file
            // {
            //   fieldname: 'filename_here',
            //   originalname: 'nhancv_dep_trai.png',
            //   encoding: '7bit',
            //   mimetype: 'image/png',
            //   destination: '/tmp/',
            //   filename: 'filename_here-1607694392023-220481630',
            //   path: '/tmp/filename_here-1607694392023-220481630',
            //   size: 5907
            // }
            const file = req.file;
            console.log(file);

            // Delete tmp
            try {
                // fs.unlinkSync(file.path);
            } catch (e) {
                // Ignore
                console.error(e);
            }
            res.json({msg: 'ok'});
        }
    });
})

Test

curl --location --request POST '<host>:<port>/uploadPhoto' \
--form 'filename_here=@"/Users/nhancv/Desktop/nhancv_dep_trai.png"'

As @Aabid told in The comments you will not need to use both, the multer middleware and upload in the controller.

You can use:

app.post('/editPhoto', upload.single('avatar'), (req, res, next) => {
   // here in the req.file you will have the uploaded avatar file
})

Or you can use:

app.post('/editPhoto', (req, res, next) => {
  upload(req, res, function (err) {
    if (err) {
      // This is a good practice when you want to handle your errors differently

      return
    }

    // Everything went fine 
  })
})

So you use one of the 2 methods, not both at the same time.