Debug. Build. Ship.
Master Full-Stack Engineering
Solve realistic full-stack coding challenges in a real-time terminal & sandbox.
React • Node.js • Express • TypeScript
1// server.js — Express REST Backend2import express from 'express';3import cors from 'cors';45const app = express();6app.use(cors());7app.use(express.json());89const tasks = [10 { id: 1, text: 'Configure Express CORS middleware', completed: true },11 { id: 2, text: 'Fetch /api/tasks in React useEffect', completed: true }12];1314app.get('/api/tasks', (req, res) => {15 res.json({ success: true, data: tasks });16});1718app.post('/api/tasks', (req, res) => {19 const newTask = { id: Date.now(), ...req.body };20 tasks.push(newTask);21 res.status(201).json({ success: true, data: newTask });22});2324app.listen(5000, () => {25 console.log('⚡ Server running on port 5000 via WebContainers');26});MERN Task Manager
React + Express$ npm run dev
[Express] Server running on port 5000
[Vite HMR] Ready in 95ms
[GET /api/tasks] 200 OK — 4ms
How CoderX.dev Works
From picking a full-stack challenge to running code in your browser tab in under 30 seconds.
Pick a Challenge
Choose from real-world React & Express scenarios: building REST APIs, auth middleware, state management, or debugging full-stack bugs.
Code In-Browser
Write clean React components and Express route handlers in a full VS Code-like editor equipped with IntelliSense and multi-file project tree.
Run via WebContainers
Instantly execute your Node.js backend client-side using StackBlitz WebContainers. Install real npm packages in milliseconds.
Get Instant Feedback
Run automated integration test suites that evaluate API responses, HTTP status codes, and frontend DOM state in real time.
Everything You Need to Master Full-Stack Development
Powered by browser-native WebAssembly technology for a frictionless developer experience.
Instant Boot Times
WebContainers boot full Node.js environments in milliseconds directly inside your browser tab.
Real npm Packages
Access and install any package from the npm registry—express, mongoose, zod, cors—without restrictions.
Full-Stack Integration
Practice real full-stack workflows connecting Express REST backend APIs directly with React client frontends.
No Docker or VMs
Zero remote server latency, zero container boot delays. Everything executes locally client-side via WebAssembly.
In-Browser Terminal
Full virtual shell capabilities to run scripts, execute tests, view server logs, and inspect process output.
Hot Reloading Live Preview
Instant HMR for React components and automatic live server restarts whenever Express routes change.
Designed for Real-World MERN Development
Tailored challenges designed to take you from syntax understanding to full-stack mastery.
Building REST APIs
Implement Express routing, middleware validation with Zod/Joi, status codes, and error handling pipelines directly in your browser.
Connecting Frontend to Backend
Master asynchronous fetch calls, React Query caching, state management, and resolving CORS issues in realistic full-stack applications.
Debugging & Refactoring
Diagnose broken MERN codebases, fix silent unhandled promise rejections, memory leaks, and subtle async route handler bugs.
Full-Stack Interview Prep
Solve timed live coding challenges modeled after senior MERN stack technical interviews at top technology companies.
An Open Platform in Its Early Stages
CoderX.dev is a labor of love built to make browser-native full-stack learning accessible. We need your feedback and support to grow.
Early Stage Platform
CoderX.dev is currently in its early stages of development. We're actively building the compiler pipeline, writing tests, and fixing bugs to provide a reliable, zero-config workspace.
Community-Driven
Since this is an open effort, we need a lot of support from the community. Sharing the platform, contributing challenges, and reporting runtime bugs helps us improve the developer experience.
No Legal Team
We don't have a legal team. This is a passion project built in public to help developers practice MERN stack. We rely on the good faith and collaborative support of the community.
Ready to Master Real MERN Development?
Start building Express backends and React frontends directly in your browser tab with WebContainers today.