React Machine Coding: Build a File Upload Component (Drag & Drop)🫳📄

Publicado em: 18 Agosto 2026
no canal de: Cooking The Code

The click-to-select part of a file upload is easy. The drag-and-drop functionality is where things get interesting. 👀

In this React machine coding project, we'll build a complete file upload component from scratch — without any libraries.

By the end of the video, you'll have a file upload component that supports:

📁 Click to browse and select a file
🖱️ Drag and drop files
📄 Display the file name
📦 Display the formatted file size
❌ Remove the selected file
✨ Visual feedback while dragging

More importantly, we'll understand how drag and drop actually works in React, including `onDragOver`, `onDragLeave`, `onDrop`, and why `e.preventDefault()` is critical.

🚀 What You'll Learn

→ Build the file upload/drop zone UI from scratch
→ Hide the native file input and trigger it using `useRef`
→ Programmatically open the file picker
→ Store the selected file using `useState`
→ Display the file name and formatted file size
→ Implement the remove file functionality
→ Understand `onDragOver`, `onDragLeave` and `onDrop`
→ Understand why `e.preventDefault()` is necessary
→ Add visual feedback when a file is dragged over the drop zone

No libraries. No pre-built components. Just React.

⏱️ Timestamps

00:00 — Final Demo
00:51 — Project Setup
01:05 — Static UI: Drop Zone Structure
01:42 — Hidden File Input + useRef
04:50 — Tracking the Selected File with useState
07:23 — File Name, File Size & Remove Functionality
10:27 — Adding Drag & Drop
16:48 — Styling the Component
17:42 — Final Demo
18:07 — Outro

💡 Why Build This?

File upload components are a great React machine coding interview problem because they test much more than just JSX.

You'll work with state, refs, browser events, file APIs, drag-and-drop events, and conditional rendering — all in one practical project.

If you're preparing for React interviews or frontend machine coding rounds, this is a project worth building yourself.

👇 Try building it yourself before watching the solution and let me know in the comments:

What React machine-coding problem should we build next?

🔔 Subscribe to Cooking the Code for weekly React, JavaScript and frontend interview content.

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