Fix JS Drag-Drop Directory Upload

My web application's existing JavaScript code needs fixing to enable folder directory uploads via drag and drop.

Key Requirements:
- Troubleshoot and fix current JavaScript code
- Ensure functionality works across Google Chrome, Mozilla Firefox, and Safari
- Implement robust drag-and-drop upload feature

Ideal Skills:
- Proficient in JavaScript and web application development
- Familiar with debugging and troubleshooting code
- Experience with cross-browser compatibility issues

Please note, the current code is implemented using plain JavaScript (not a specific framework like React or Vue.js).