dropzone to S3

How to use the dropzone element to upload files directly to an AWS S3 bucket.

This page is still under development


If you want your users to upload large files, S3 is a great option. However, it can be tricky to navigate because of how it is secure by default. The Dropzone uploader wants to be able to push a file to a URL endpoint, but S3 doesn't provide that for security purposes. Other techniques suggest using a Lambda function to generate that signed URL, which is possible. However, this guide will focus on using the AWS JavaScript SDK to upload directly from a browser.

The method that will be outlined on this page is advanced and not directly supported by BetterForms. These techniques were compiled from around the internet and are implemented into BetterForms by taking advantage of how BetterForms exposes HTML and JavaScript in the page editor

Configuring AWS

If you don't already have an AWS account, sign up here.

1. Amazon Cognito

Amazon Cognito is the user management service that we'll use to authenticate our application to AWS for uploading. Cognito allows for us to configure permissions for anonymous users, which will be useful in this case so that we don't have to worry about user credentials when uploading to our bucket.

  1. From the AWS Console, navigate to the Cognito service.

  2. Make sure you're in your preferred region (Cognito is not available in all regions)

  3. Create a new Identity Pool

  4. Be sure to check the box labeled Enable access to unauthenticated identities. All other settings can be left at default, then click Create Pool

  5. The next page will create new roles in IAM for this identity pool. Simply click Allow to continue.

  6. In the final confirmation screen, make note of your Identity Pool ID.

2. Configuring your S3 bucket

Let's create a new bucket for you uploads. Since this bucket will have public access, it's good to make a separate bucket so that you can isolate data concerns.

  1. From the AWS Console, navigate to the S3 service.

  2. Create a new bucket. Make sure that it's configured in the same region as your Cognito Identity Pool that was setup in step 1.

  3. When configuring the bucket, all settings can be left at their defaults.

  4. Navigate to the bucket, then to the Permissions tab.

  5. In the CORS configuration section, add the following code. This will allow any browser to send a PUT request to your bucket, which is how the upload works

<?xml version="1.0" encoding="UTF-8"?>
<CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/">

3. Configuring IAM policy

Lastly, we need to configure the policy for Cognito Role that we created in step 1 to have write access to the bucket we created in step 2.

  1. From the AWS Console, navigate to the IAM service.

  2. In the sidebar, click on Roles and locate the Unauth role that was created for your Cognito Identity Pool. It should follow a pattern like Cognito_appnameUnauth_Role where appname is the name you gave to your Identity Pool.

  3. Choose the option to Add inline policy, then navigate to the JSON tab and paste in the following code. These are the absolute minimal settings that will allow this anonymous user to put things into the bucket but nothing else.

    "Version": "2012-10-17",
    "Statement": [
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": [
            "Resource": [

Make sure you change the example-bucket in lines 17-18 with the name of your own bucket

Now we're ready to go back to BetterForms! Feel free to navigate back to S3 and keep it open in a new tab for inspection of your files as we upload them...

Configuring your Site Settings

Since this method requires external libraries not provided by BetterForms, you'll need to inject them into your site using a DOM Header Insertion.

<script src="https://cdnjs.cloudflare.com/ajax/libs/aws-sdk/2.543.0/aws-sdk.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/dropzone/5.2.0/min/dropzone.min.js"></script>
<link href="https://cdnjs.cloudflare.com/ajax/libs/dropzone/5.2.0/min/dropzone.min.css" rel="stylesheet">

These libraries may have been updated since the time of this writing, check the original sources for the most updated CDN links.

Configuring your Page

Now that you have your AWS bucket and credentials setup, you can plug in your values to the example page to see this in action. The rest of this guide assumes that you have duplicated that page into your own site so that you have access to the JavaScript and HTML code there.


To insert the Dropzone element in your page, we'll use an HTML element. The id of myDZ is the most crucial piece, and is how we will target this element using the JavaScript.

<form id="myDZ" action="/file-upload" class="vue-dropzone dropzone">
  <div class="fallback">
    <input name="file" type="file" multiple />
  <div class="dz-message text-center">
      <!-- Customize this div with your own elements -->
      <h1>Drop your file here, or click to browse</h1>


To initialize the dropzone, you need to run some JavaScript code that programmatically configures all of the settings. I recommend doing this in a named action on the page so that you can call it at a specific place in your users workflow if necessary. In my testing, I found that putting this code in the onFormLoad named action works about half of the time because sometimes the code runs before the page is fully rendered and therefore cannot be attached to the form.

See the full code in the initDZ named action on the example page.

The first few lines of this code is where you'll configure with your settings from AWS. Feel free to hard-code these value into the JavaScript function instead of referencing model unless you want to programmatically change them later.

Your bucketRegion should match the start of your Identity Pool ID. For example, if your Identity Pool ID is us-west-2:5fxxxxxxx-2696-4xxxx-8xxxxxx-dxxxxxxxx then your bucket region would be us-west-2

var bucketName = model.settings.bucketName;
// var bucketName = 'example-bucket';   <-- for hard coding, use quotes
var bucketRegion = model.settings.region;
var IdentityPoolId = model.settings.identityPool;

For the options variable, see the Dropzone documentation if you'd like to further customize the element.

If you follow along with the code, you'll notice that I'm adding files to an array as they are added to the dropzone and moving them to a different array when the upload is complete. Finally, the named action called onDropzoneComplete runs when all the files have uploaded. This is where you can run a Utility Hook back to your FMS to save the data in your database.

Be sure to leave the default keys in the Data Model when duplicating the example page. These keys are directly referenced by the JavaScript code and it may fail if these keys do not exist.

Manipulating the Queue

Since we are adding this element completely from scratch, we have to do a little bit more work to interact with the dropzone. It's not integrated into Vue like the rest of the elements you may be used to in BetterForms, so we have to use regular JavaScript functions to work with it.

The following 3 lines of code is how the Dropzone is initialized.

// bind the events to the Dropzone so that Dropzone will callback our functions
// when it's done with certain tasks (see Dropzone Events docs)
Dropzone.prototype.uploadFiles = files => files.map(sendEvents);

// initilaize the dropzone based on the id 'myDZ' and options provided
var dz = new Dropzone('#myDZ', options)

// store the dropzone object at the window level so it
// can be referenced globally by other actions
window.dz = dz

If you keep reading the code in the demo file, you'll see several dz.on(...) functions. These functions are the events called when things happen in the dropzone element. One example is the addedfile event, which is called when a file is added to the dropzone:

dz.on("addedfile", function(file) {

This simple function pushes the uuid key of the file that is passed into this function to an array so that you can better work with the queue using Vue.

In production, it's better to pass the entire file object into an array so that you can get at more details of the file object instead of just the uuid. The reason it's setup like this for the demo is because the entire file object cannot be printed on screen as code. Once you fully understand how to manipulate the queue, be sure to update all references to this array (it's also used in the removedFile event, for example)

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