Sending additional data with programatically created Dropzone using the sending event

All we need is an easy explanation of the problem, so here it is.

I have the following (simplified for example) angular directive which creates a dropzone

directives.directive('dropzone', ['dropZoneFactory', function(dropZoneFactory){
    'use strict';
    return {
        restrict: 'C',
        link : function(scope, element, attrs){

            new Dropzone('#', {url: attrs.url});

            var myDropZone = Dropzone.forElement('#';

            myDropZone.on('sending', function(file, xhr, formData){
                //this gets triggered

As you can see the the sending event handler I’m trying to send the username (“bob”) along with the uploaded file. However, I can’t seem to retrieve it in my route middleware as req.params comes back as an empty array (I’ve also tried req.body).

My node route

    path: '/uploads',
    httpMethod: 'POST',
    middleware: [express.bodyParser({ keepExtensions: true, uploadDir: 'uploads'}),function(request,response){
        // comes back as []

        //this sees the files fine

        response.end("upload complete");

Here is what the docs say on the sending event

Called just before each file is sent. Gets the xhr object and the formData objects as second and third parameters, so you can modify them (for example to add a CSRF token) or add additional data.


I dropped the programmatic approach for now. I have two forms submitting to the same endpoint, a regular one with just post and a dropzone one. Both work, so I don’t think it’s an issue with the endpoint rather with how I handle the ‘sending’ event.

//Receives the POST var just fine
form(action="", method="post", id="mydz")
    input(type="hidden", name="additionaldata", value="1")

//With this one I can get the POST var
form(action="", method="post", id="mydz2", class="dropzone")
    input(type="hidden", name="additionaldata", value="1")

How to solve :

I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.

Method 1

OK, I’ve actually figured it out, thanks to Using Dropzone.js to upload after new user creation, send headers

The sending event:

        myDropZone.on('sending', function(file, xhr, formData){
            formData.append('userName', 'bob');

As opposed to formData.userName = 'bob' which doesn’t work for some reason.

Method 2

I would like to add to NicolasMoise’s answer.
As a beginner in webdev I got stuck on how to obtain an instance of Dropzone. I wanted to retrieve an instance of Dropzone that had been generated by the autodiscovery feature. But it turns out that the easiest way to do this is to manually add a Dropzone instance after first telling Dropzone not to auto-discover.

<input id="pathInput"/>
<div id="uploadForm" class="dropzone"/> 
    Dropzone.autoDiscover = false;
    var dZone = new Dropzone("div#uploadForm", {url: "/api/uploads"});
    dZone.on("sending", function(file, xhr, data){
      data.append("uploadFolder", $("#pathInput")[0].value);

Serverside the data will be in request.body.uploadFolder

Method 3

Nicolas answer is one possible solution to the problem. It is especially useful if you need to alter the file object prior to sending.

An alternative is to use the params option:

var myDropzone = new Dropzone("div#myId", 
                              { url: "/file/post", params: { 'param_1': 1 }});

cf. the documention

Method 4

For those that are using thatisuday/ng-dropzone the callback methods are done as such:

    <ng-dropzone class="dropzone" options="dzOptions" callbacks="dzCallbacks" methods="dzMethods"></ng-dropzone>

In a controller:

    $scope.dzCallbacks = {
        sending: function(file, xhr, form) {
            console.log('custom sending', arguments);
            form.append('a', 'b');

Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂

All methods was sourced from or, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

Leave a Reply