[EMB-60] Prevent user from selecting multiple files when clicking upload button.

CHANGELOG.md

@@ -49,6 +49,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Margins for scrollbar on `file-browser`
 - Clickability on dropzone widget
 - Handle Dropzone enable/disable properly
+- Prevent users from selecting multiple files by clicking 'Upload' button in Quickfiles
 
 ## [0.12.4] - 2017-12-04
 ### Added

addon/components/dropzone-widget/component.js

@@ -80,6 +80,13 @@ export default Ember.Component.extend({
             }
         });
 
+        // Dropzone.js does not have an option for disabling selecting multiple files when clicking the "upload" button.
+        // Therefore, we remove the "multiple" attribute for the hidden file input element, so that users cannot select
+        // multiple files for upload in the first place.
+        if (this.get('options.preventMultipleFiles') && this.get('clickable')){
+            Ember.$('.dz-hidden-input').removeAttr('multiple');
+        }
+
         this.set('dropzoneElement', drop);
 
         // Set osf session header