3001.md
root@localhost:~# cat 3001.md

Localhost:3001 React Development Port

# 定义

Port 3001 naturally emerged as the next logical choice when port 3000 is unavailable in React development workflows. Most React development tools, including Create React App, automatically increment to port 3001 when port 3000 is occupied. This port maintains familiarity within the 3000-series range while providing separation for multiple concurrent development processes. It's particularly valuable in full-stack development and microservices architectures.

# Services and Software That Use Port 3001

## React Applications

• Create React App Secondary
Additional React applications when the primary app occupies port 3000.
• Next.js Secondary Instance
Secondary Next.js applications for A/B testing or multi-tenant development.
• React Microservices
Individual React-based microservice frontends in distributed architectures.

## Development Tools

• Storybook Alternative
Storybook component development environment when configured on alternative port.
• React DevTools Server
Development utilities and debugging tools for React applications.
• Hot Reload Proxy
Development proxy servers for enhanced hot reloading capabilities.

## Full-Stack Development

• Frontend-Backend Separation
Frontend React app on 3001 while backend API runs on different port.
• Multi-Environment Testing
Different environment versions running simultaneously for comparison.
• Component Libraries
Standalone component library development and testing environments.

## Other Tools

• Mock API Servers
Development mock servers serving static or dynamic test data.
• Webpack Dev Server
Custom webpack configurations running on alternative ports.
• Testing Environments
Isolated testing environments for CI/CD and automated testing.

# Frequently Asked Questions

Q: How do I access localhost:3001?

A:

Start your React app with 'PORT=3001 npm start' or let Create React App auto-assign the port, then open http://localhost:3001 in your browser.

Q: When should I use port 3001 instead of 3000?

A:

Use port 3001 when port 3000 is occupied, when running multiple React applications simultaneously, or when separating different environments or services.

Q: How do I run multiple React apps on ports 3000 and 3001?

A:

Start the first app normally (port 3000), then start the second with 'PORT=3001 npm start' or let Create React App auto-detect and suggest port 3001.

Q: How to fix CORS issues when React app runs on port 3001?

A:

Add a 'proxy' field to package.json pointing to your API server, or configure your backend to allow requests from localhost:3001 in CORS settings.

Q: How to set different environment variables for port 3001?

A:

Create separate .env files (.env.development, .env.3001) or use scripts like 'PORT=3001 REACT_APP_ENV=secondary npm start' for port-specific configuration.

Q: Should I deploy React apps using port 3001?

A:

No, port 3001 is for development only. In production, build with 'npm run build' and serve through a web server on standard ports 80/443.

Q: Why isn't hot reload working on localhost:3001?

A:

Check WebSocket connectivity, ensure firewall allows port 3001, verify you're accessing the correct URL, and try clearing browser cache or restarting the dev server.

Q: How to easily switch between ports 3000 and 3001?

A:

Create npm scripts like 'start:alt': 'PORT=3001 npm start' in package.json, or use environment files to manage different port configurations.

# How to Use Port 3001

1.

Check Port Availability

Verify that port 3001 is available and understand why port 3000 is occupied.

bash
lsof -i :3001
2.

Start React App on Port 3001

Use environment variable or command line flag to specify port 3001 for your React application.

bash
PORT=3001 npm start
3.

Alternative: Create React App Auto-Assignment

Let Create React App automatically detect port conflict and offer to use port 3001.

bash
npm start
4.

Verify Application Access

Test that your React application is accessible on port 3001 and functioning correctly.

bash
curl http://localhost:3001
5.

Configure Development Environment

Update your .env file, scripts, and documentation to reflect port 3001 configuration for consistency.

# Common Problems

## MEDIUM Severity Issues

⚠ Port Confusion Between 3000 and 3001

Developers accessing wrong port or mixing up which application runs on which port during multi-project development.

⚠ Hot Reloading Issues

Hot module replacement not working properly on port 3001, causing development workflow disruption.

⚠ Environment Variable Conflicts

Multiple React applications interfering with each other's environment variables and configuration.

## HIGH Severity Issues

⚠ API Communication Problems

Frontend on port 3001 unable to communicate with backend APIs due to CORS or hardcoded URL issues.

## LOW Severity Issues

⚠ Browser Cache Confusion

Browser caching causing confusion between applications running on ports 3000 and 3001.

# Troubleshooting Solutions

## All Platform

Fix Cross-Port API Communication

For: API Communication Problems

Steps:

  1. Configure proxy settings in package.json for API calls
  2. Set up CORS headers on backend to allow port 3001
  3. Use environment variables for API base URLs
  4. Test API connectivity from port 3001
all
echo '"proxy": "http://localhost:3000"' >> package.json

Fix Cross-Port API Communication

For: API Communication Problems

Steps:

  1. Configure proxy settings in package.json for API calls
  2. Set up CORS headers on backend to allow port 3001
  3. Use environment variables for API base URLs
  4. Test API connectivity from port 3001
all
REACT_APP_API_URL=http://localhost:3000 npm start

Fix Hot Module Replacement on Port 3001

For: Hot Reloading Issues

Steps:

  1. Ensure WebSocket connections are working properly
  2. Check firewall settings for port 3001
  3. Verify React development server configuration
  4. Clear browser cache and restart development server
all
PORT=3001 FAST_REFRESH=true npm start

Fix Hot Module Replacement on Port 3001

For: Hot Reloading Issues

Steps:

  1. Ensure WebSocket connections are working properly
  2. Check firewall settings for port 3001
  3. Verify React development server configuration
  4. Clear browser cache and restart development server
all
rm -rf node_modules/.cache && PORT=3001 npm start

# Summary

root@localhost:~# echo "Port 3001 Documentation Complete"

What it is: localhost:3001 is Localhost:3001 is commonly used as an alternative React development port when port 3000 is already occupied. It serves as a secondary development port for React applications, microservices, and multi-project development environments where multiple React or Node.js services need to run simultaneously.

Who uses it: Create React App Secondary, Next.js Secondary Instance, React Microservices, Storybook Alternative, React DevTools Server, Hot Reload Proxy, Frontend-Backend Separation, Multi-Environment Testing, Component Libraries, Mock API Servers, Webpack Dev Server, Testing Environments

Access URL: http://localhost:3001