Error handling when uploading file using multer with expressjs

This is how to write multer middleware that handle upload and errors

const multer = require("multer");function uploadFile(req, res, next) {    const upload = multer().single('yourFileNameHere');    upload(req, res, function (err) {        if (err instanceof multer.MulterError) {            // A Multer error occurred when uploading.        } else if (err) {            // An unknown error occurred when uploading.        }        // Everything went fine.         next()    })}

You can handle errors using the onError option:

app.post('/upload',[  multer({    dest    : './uploads/',    onError : function(err, next) {      console.log('error', err);      next(err);    }  }),  function(req, res) {    res.status(204).end();  }]);

If you call next(err), your route handler (generating the 204) will be skipped and the error will be handled by Express.

I think (not 100% sure as it depends on how multer is implemented) that your route handler will be called when the file is saved. You can use onFileUploadComplete to log a message when the upload is done, and compare that to when your route handler is called.

Looking at the code, multer calls the next middleware/route handler when the file has been uploaded completely.

Try this

var upload = multer().single('avatar')app.post('/profile', function (req, res) {  upload(req, res, function (err) {    if (err) {      // An error occurred when uploading       return    }    // Everything went fine   })}

ref :

http://wiki.workassis.com/nodejs-express-get-post-multipart-request-handling-example/

https://www.npmjs.com/package/multer#error-handling