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Dropzone with an Express Backend


The uploader behaviour for Dropzone changed from previous versions, making the links to sample code in the Dropzone documentation outdated ( I only discovered the change after updating to a new version of a site template that I was using - and seeing that my previous working code stopped working... )

The following works with the following (fairly current) versions : Dropzone v4.3.0, Express v4.13.4

In the GUI

<link href="/t/css/plugins/dropzone/dropzone.css" rel="stylesheet"/>
<form id="my-awesome-dropzone" action="" method="post" enctype="multipart/form-data" class="dropzone">
  <div class="fallback">
    <input name="source_file[]" type="file" multiple="multiple"/>
  <div class="form-group pull-right">
    <button id="batch-upload" type="submit" class="btn btn-danger">Upload Now! </button>
<script src="/t/js/plugins/dropzone/dropzone.js"></script>
$(document).ready(function() {

    Dropzone.options.myAwesomeDropzone = {
      autoProcessQueue: false,
      //paramName:'source_file', // Name used to transfer the file(s) (will have '[i=0,1,2,3,4...]' appended)
      paramName: function(n) { return 'source_file[]';},  // Don't enumerate the transfers
      uploadMultiple: true,
      parallelUploads: 4,  // default is 2
      //maxFilesize: 2, // MB

      init: function() {
        var myDropzone = this;
        this.on("completemultiple", function(files, response) {  // was queuecomplete

          // Now reload page...
          location.reload(true);  // true => force server reload

        this.on("addedfile", function() {
          console.log("Added File! - show the upload button");

        $('#batch-upload').click( function(e) {
          console.log("Clicked on upload button"); // ,






On the Express server

var express = require('express');
var upload_files = require('multer')();

// .. regular set-up for 'app' ..'/batch/upload', upload_files.array('source_file[]'), process_upload);

var Promise = require('bluebird');
var fs = Promise.promisifyAll(require('fs'));
var path = require('path');
var sanitize = require("sanitize-filename");

function process_upload(req, res) {
  if(req.files) {
    console.log("req.files.length = ", req.files.length);

    var upload_dir='uploads';  //somewhere relevant

      .each(function(file_incoming, idx) {
          console.log("  Writing POSTed data :", file_incoming.originalname);
          var sanitized_filename = sanitize(file_incoming.originalname);
          var file_to_save = path.join( upload_dir, sanitized_filename );

          return fs
            .writeFileAsync(file_to_save, file_incoming.buffer)
      // .catch() code not included for clarity : Clearly you'll need to do some error checking...
      .then( _ => {
        console.log("Added files : Success");
        return res.sendStatus(200);