Did you mean to visit localhost:4200?

Did you mean to visit: http://localhost:4200/?

💡 Pro Tip: Port 4200 is Angular's default development port. If it's busy, Angular CLI will automatically suggest the next available port like 4201.

Quick Commands for Port 4200

Find what's using port 4200:
lsof -i :4200 (Mac/Linux)
netstat -ano | findstr :4200 (Windows)
Start Angular on different port:
ng serve --port 4201
npm start -- --port 4201

About Port 4200

Port 4200 is commonly used by:

Common Issues with Port 4200

"Port 4200 is already in use"

This error occurs when another application is already using port 4200. Solutions:

  • Find and close the application using port 4200
  • Use a different port:
    • Angular CLI: ng serve --port 4201
    • In angular.json: Set "port": 4201 in the serve options
  • On Windows, find and kill the process: netstat -ano | findstr :4200 then taskkill /PID [PID] /F
  • On Linux/Mac: lsof -i :4200 then kill -9 [PID]

"Cannot access localhost:4200 from other devices"

By default, Angular's development server only listens on localhost:

  • To make it accessible from other devices on your network: ng serve --host 0.0.0.0
  • Then access it using your computer's IP address: http://YOUR_IP:4200

"Changes not reflecting in the browser"

If your code changes aren't showing up:

  • Check if the Angular development server is running with hot reload enabled
  • Try clearing your browser cache
  • Restart the development server with ng serve
  • Check for errors in the terminal or browser console

Related Ports You Might Need

🅰️ Angular Development Best Practices

Comprehensive guide for Angular development on port 4200

Project Setup & Configuration

  • ng new my-app - Create new Angular project
  • ng generate component my-component - Generate component
  • ng generate service my-service - Generate service
  • Configure angular.json for development
  • Set up package.json dependencies

Development Server Commands

  • ng serve - Start development server (port 4200)
  • ng serve --port 4201 - Use different port
  • ng serve --host 0.0.0.0 - Network access
  • ng serve --open - Auto-open browser
  • ng serve --poll=2000 - Polling for changes

Build & Deployment

  • ng build - Production build
  • ng build --prod - Optimized build
  • ng build --watch - Watch mode
  • ng test - Run unit tests
  • ng e2e - Run end-to-end tests

Debugging & Testing

  • Use Angular DevTools browser extension
  • Configure source maps in tsconfig.json
  • Use console.log() and browser DevTools
  • Set up breakpoints in TypeScript files
  • Use Angular testing utilities

🏗️ Angular Architecture & Patterns

Best practices for Angular application architecture and design patterns

Component Architecture

  • Smart vs Presentational components
  • Component communication patterns
  • Lifecycle hooks implementation
  • Change detection strategies
  • OnPush change detection

State Management

  • NgRx for complex state management
  • RxJS observables and subjects
  • BehaviorSubject for shared state
  • Service-based state management
  • Local component state

Routing & Navigation

  • Lazy loading modules
  • Route guards implementation
  • Child routes and nested routing
  • Route resolvers for data
  • Navigation events handling

Performance Optimization

  • OnPush change detection
  • TrackBy functions for *ngFor
  • Pure pipes for calculations
  • Lazy loading strategies
  • Bundle size optimization

🛠️ Angular Development Tools

Essential tools and extensions for Angular development

IDE Extensions

  • Angular Language Service (VS Code)
  • Angular Snippets extension
  • TypeScript Importer
  • Prettier for code formatting
  • ESLint for code linting

Browser DevTools

  • Angular DevTools extension
  • Augury (legacy Angular tool)
  • Chrome DevTools for debugging
  • Network tab for API calls
  • Performance profiling

Testing Tools

  • Jasmine for unit testing
  • Karma test runner
  • Protractor for e2e testing
  • Cypress for modern e2e testing
  • Testing utilities and mocks

Build & Deployment

  • Angular CLI build system
  • Webpack configuration
  • Docker containerization
  • CI/CD pipeline setup
  • Environment configuration

⚡ Angular Performance & Optimization

Optimize your Angular applications for better performance and user experience

Change Detection Optimization

Optimize Angular's change detection:

  • Use OnPush change detection strategy
  • Implement trackBy functions for *ngFor
  • Use pure pipes for calculations
  • Detach change detection when needed
  • Use async pipe for observables

Bundle Size Optimization

Reduce application bundle size:

  • Enable production mode builds
  • Use tree shaking effectively
  • Implement lazy loading modules
  • Analyze bundle with webpack-bundle-analyzer
  • Use dynamic imports for code splitting

Runtime Performance

Improve runtime performance:

  • Optimize template expressions
  • Use OnPush strategy for components
  • Implement virtual scrolling for large lists
  • Use Web Workers for heavy computations
  • Optimize API calls and caching

Development Performance

Speed up development workflow:

  • Use Angular CLI with --poll option
  • Configure TypeScript compilation
  • Use incremental builds
  • Optimize IDE performance
  • Use hot module replacement

🧪 Angular Testing & Quality Assurance

Comprehensive testing strategies for Angular applications

Unit Testing

  • ng test - Run unit tests
  • Component testing with TestBed
  • Service testing with dependency injection
  • Pipe testing strategies
  • Mock services and dependencies

Integration Testing

  • Component integration tests
  • Module testing strategies
  • Routing integration tests
  • Form validation testing
  • API integration testing

E2E Testing

  • ng e2e - Run end-to-end tests
  • Protractor configuration
  • Cypress for modern e2e testing
  • User journey testing
  • Cross-browser testing

Quality Assurance

  • Code coverage reporting
  • Linting with ESLint and TSLint
  • Prettier for code formatting
  • Husky for pre-commit hooks
  • CI/CD pipeline integration

Useful Resources

📋 Port 4200 Development Summary

Port 4200 is the standard development port for Angular applications, serving as the default when using Angular CLI's development server. It's designed to provide a fast, efficient development environment with features like hot module replacement, live reload, and optimized builds for rapid iteration and testing.

Angular's development server on port 4200 offers comprehensive tooling for modern web development, including TypeScript compilation, template compilation, and integration with various testing frameworks. Understanding its configuration, optimization techniques, and best practices is essential for building scalable, maintainable Angular applications.

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