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Master Full-Stack Engineering

Solve realistic full-stack coding challenges in a real-time terminal & sandbox.
React • Node.js • Express • TypeScript

coderx-challenge-04
1// server.js — Express REST Backend
2import express from 'express';
3import cors from 'cors';
4
5const app = express();
6app.use(cors());
7app.use(express.json());
8
9const tasks = [
10 { id: 1, text: 'Configure Express CORS middleware', completed: true },
11 { id: 2, text: 'Fetch /api/tasks in React useEffect', completed: true }
12];
13
14app.get('/api/tasks', (req, res) => {
15 res.json({ success: true, data: tasks });
16});
17
18app.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});
23
24app.listen(5000, () => {
25 console.log('⚡ Server running on port 5000 via WebContainers');
26});
http://localhost:3000/
LIVE PREVIEW

MERN Task Manager

React + Express
Configure Express CORS middleware200 OK
Fetch /api/tasks in React useEffect200 OK
Implement JWT auth route handler200 OK
Terminal

$ npm run dev

[Express] Server running on port 5000

[Vite HMR] Ready in 95ms

[GET /api/tasks] 200 OK — 4ms

WORKFLOW

How CoderX.dev Works

From picking a full-stack challenge to running code in your browser tab in under 30 seconds.

01

Pick a Challenge

Choose from real-world React & Express scenarios: building REST APIs, auth middleware, state management, or debugging full-stack bugs.

Interactive Tasks
02

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.

VS Code Editor
03

Run via WebContainers

Instantly execute your Node.js backend client-side using StackBlitz WebContainers. Install real npm packages in milliseconds.

Real Node.js Engine
04

Get Instant Feedback

Run automated integration test suites that evaluate API responses, HTTP status codes, and frontend DOM state in real time.

Automated Testing
PLATFORM CAPABILITIES

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.

PRACTICE SCENARIOS

Designed for Real-World MERN Development

Tailored challenges designed to take you from syntax understanding to full-stack mastery.

Express / Node.js
Backend Engineering

Building REST APIs

Implement Express routing, middleware validation with Zod/Joi, status codes, and error handling pipelines directly in your browser.

app.get('/api/users')express.json()Zod Schema Validation
React + Express
Full-Stack Integration

Connecting Frontend to Backend

Master asynchronous fetch calls, React Query caching, state management, and resolving CORS issues in realistic full-stack applications.

useEffect() FetchingCORS ConfigurationState Management
Real Bug Scenarios
Problem Solving

Debugging & Refactoring

Diagnose broken MERN codebases, fix silent unhandled promise rejections, memory leaks, and subtle async route handler bugs.

Async Middleware FixesMemory Leak PreventionStatus Code Audits
Top Tech Assessments
Career Growth

Full-Stack Interview Prep

Solve timed live coding challenges modeled after senior MERN stack technical interviews at top technology companies.

Timed Coding DrillsJWT Auth ImplementationDatabase Schema Design
PLATFORM STATUS & SUPPORT

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.

GET STARTED IN SECONDS

Ready to Master Real MERN Development?

Start building Express backends and React frontends directly in your browser tab with WebContainers today.

No Credit Card RequiredInstant Browser IDEInteractive Challenges