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Chapter 14: JavaScript Server-Sent Events - Complete Guide to Real-time Data Push

Server-Sent Events (SSE) is a web standard that enables servers to push data to web browsers in real-time over a single HTTP connection. Unlike WebSocket, SSE is unidirectional (server-to-client only) and is perfect for live updates, notifications, and real-time data streaming.

Why Server-Sent Events is Essential in JavaScript​

Server-Sent Events in JavaScript is crucial because it:

  • Enables Real-time Updates: Provides instant server-to-client data push
  • Simplifies Implementation: Easier to implement than WebSocket for one-way communication
  • Supports Automatic Reconnection: Built-in reconnection mechanism
  • Works with HTTP: Uses standard HTTP connections, no special protocols
  • Enables Live Applications: Perfect for live feeds, notifications, and real-time dashboards
  • Reduces Server Load: More efficient than polling for real-time data

Learning Objectives​

Through this chapter, you will master:

  • EventSource API and basic SSE implementation
  • Real-time data streaming and event handling
  • Error handling and reconnection strategies
  • Advanced SSE patterns and best practices
  • Building live applications with SSE
  • Performance optimization and security considerations

Basic Server-Sent Events​

EventSource API​

// Basic EventSource connection
const eventSource = new EventSource('/api/events');

// Handle connection open
eventSource.onopen = function(event) {
  console.log('SSE connection opened');
  console.log('Ready state:', eventSource.readyState);
};

// Handle incoming messages
eventSource.onmessage = function(event) {
  console.log('Received message:', event.data);
  console.log('Event type:', event.type);
  console.log('Last event ID:', event.lastEventId);
  
  // Parse JSON data if needed
  try {
    const data = JSON.parse(event.data);
    handleMessage(data);
  } catch (error) {
    console.log('Received text message:', event.data);
  }
};

// Handle connection errors
eventSource.onerror = function(event) {
  console.error('SSE connection error:', event);
  
  switch (eventSource.readyState) {
    case EventSource.CONNECTING:
      console.log('Reconnecting...');
      break;
    case EventSource.CLOSED:
      console.log('Connection closed');
      break;
  }
};

// Close connection
function closeConnection() {
  eventSource.close();
}

// Helper function to handle different message types
function handleMessage(data) {
  switch (data.type) {
    case 'notification':
      showNotification(data.message);
      break;
    case 'update':
      updateData(data.payload);
      break;
    case 'status':
      updateStatus(data.status);
      break;
    default:
      console.log('Unknown message type:', data.type);
  }
}

Event Types and Custom Events​

// EventSource with custom event types
const eventSource = new EventSource('/api/events');

// Handle specific event types
eventSource.addEventListener('user-notification', function(event) {
  console.log('User notification:', event.data);
  const notification = JSON.parse(event.data);
  displayNotification(notification);
});

eventSource.addEventListener('system-update', function(event) {
  console.log('System update:', event.data);
  const update = JSON.parse(event.data);
  applySystemUpdate(update);
});

eventSource.addEventListener('data-stream', function(event) {
  console.log('Data stream:', event.data);
  const data = JSON.parse(event.data);
  updateDataStream(data);
});

eventSource.addEventListener('heartbeat', function(event) {
  console.log('Heartbeat received');
  updateLastHeartbeat();
});

// Handle all messages (fallback)
eventSource.onmessage = function(event) {
  console.log('Default message handler:', event.data);
};

// Display notification
function displayNotification(notification) {
  const notificationElement = document.createElement('div');
  notificationElement.className = 'notification';
  notificationElement.innerHTML = `
    <h4>${notification.title}</h4>
    <p>${notification.message}</p>
    <span class="timestamp">${new Date().toLocaleTimeString()}</span>
  `;
  
  document.getElementById('notifications').appendChild(notificationElement);
  
  // Auto-remove after 5 seconds
  setTimeout(() => {
    notificationElement.remove();
  }, 5000);
}

// Update data stream
function updateDataStream(data) {
  const dataContainer = document.getElementById('dataStream');
  dataContainer.innerHTML = `
    <div class="data-item">
      <span class="label">Value:</span>
      <span class="value">${data.value}</span>
    </div>
    <div class="data-item">
      <span class="label">Timestamp:</span>
      <span class="value">${new Date(data.timestamp).toLocaleString()}</span>
    </div>
  `;
}

Advanced SSE Patterns​

SSE Manager Class​

class SSEManager {
  constructor(url, options = {}) {
    this.url = url;
    this.options = {
      withCredentials: false,
      reconnectInterval: 3000,
      maxReconnectAttempts: 5,
      heartbeatInterval: 30000,
      ...options
    };
    
    this.eventSource = null;
    this.reconnectAttempts = 0;
    this.heartbeatTimer = null;
    this.eventListeners = new Map();
    this.isConnected = false;
    this.lastEventId = null;
    
    this.connect();
  }
  
  connect() {
    try {
      const url = this.lastEventId ? 
        `${this.url}?lastEventId=${this.lastEventId}` : 
        this.url;
      
      this.eventSource = new EventSource(url, {
        withCredentials: this.options.withCredentials
      });
      
      this.setupEventHandlers();
    } catch (error) {
      console.error('Failed to create EventSource:', error);
      this.handleReconnect();
    }
  }
  
  setupEventHandlers() {
    this.eventSource.onopen = (event) => {
      console.log('SSE connection opened');
      this.isConnected = true;
      this.reconnectAttempts = 0;
      this.startHeartbeat();
      this.emit('open', event);
    };
    
    this.eventSource.onmessage = (event) => {
      this.lastEventId = event.lastEventId;
      this.emit('message', event);
    };
    
    this.eventSource.onerror = (event) => {
      console.error('SSE connection error:', event);
      this.isConnected = false;
      this.stopHeartbeat();
      this.emit('error', event);
      
      if (this.eventSource.readyState === EventSource.CLOSED) {
        this.handleReconnect();
      }
    };
  }
  
  handleReconnect() {
    if (this.reconnectAttempts < this.options.maxReconnectAttempts) {
      this.reconnectAttempts++;
      console.log(`Reconnecting... (${this.reconnectAttempts}/${this.options.maxReconnectAttempts})`);
      
      setTimeout(() => {
        this.connect();
      }, this.options.reconnectInterval);
    } else {
      console.error('Max reconnection attempts reached');
      this.emit('maxReconnectAttemptsReached');
    }
  }
  
  startHeartbeat() {
    this.heartbeatTimer = setInterval(() => {
      if (!this.isConnected) {
        console.log('No heartbeat received, reconnecting...');
        this.handleReconnect();
      }
    }, this.options.heartbeatInterval);
  }
  
  stopHeartbeat() {
    if (this.heartbeatTimer) {
      clearInterval(this.heartbeatTimer);
      this.heartbeatTimer = null;
    }
  }
  
  // Event system
  on(event, callback) {
    if (!this.eventListeners.has(event)) {
      this.eventListeners.set(event, []);
    }
    this.eventListeners.get(event).push(callback);
  }
  
  off(event, callback) {
    if (this.eventListeners.has(event)) {
      const listeners = this.eventListeners.get(event);
      const index = listeners.indexOf(callback);
      if (index > -1) {
        listeners.splice(index, 1);
      }
    }
  }
  
  emit(event, data) {
    if (this.eventListeners.has(event)) {
      this.eventListeners.get(event).forEach(callback => {
        callback(data);
      });
    }
  }
  
  // Add custom event listener
  addEventListener(eventType, callback) {
    if (this.eventSource) {
      this.eventSource.addEventListener(eventType, callback);
    }
  }
  
  close() {
    this.stopHeartbeat();
    if (this.eventSource) {
      this.eventSource.close();
    }
  }
}

// Usage
const sseManager = new SSEManager('/api/events');

sseManager.on('open', () => {
  console.log('Connected to SSE stream');
});

sseManager.on('message', (event) => {
  console.log('Received message:', event.data);
});

sseManager.on('error', (error) => {
  console.error('SSE error:', error);
});

sseManager.addEventListener('notification', (event) => {
  const data = JSON.parse(event.data);
  showNotification(data);
});

Real-time Dashboard​

class RealTimeDashboard {
  constructor() {
    this.sseManager = null;
    this.data = {
      users: 0,
      orders: 0,
      revenue: 0,
      alerts: []
    };
    
    this.initializeDashboard();
  }
  
  async initializeDashboard() {
    await this.setupSSE();
    this.setupUI();
    this.startPeriodicUpdates();
  }
  
  async setupSSE() {
    this.sseManager = new SSEManager('/api/dashboard/events');
    
    this.sseManager.on('open', () => {
      this.updateConnectionStatus('connected');
    });
    
    this.sseManager.on('error', () => {
      this.updateConnectionStatus('disconnected');
    });
    
    this.sseManager.on('message', (event) => {
      this.handleDashboardUpdate(event);
    });
    
    // Handle specific event types
    this.sseManager.addEventListener('user-count', (event) => {
      const data = JSON.parse(event.data);
      this.updateUserCount(data.count);
    });
    
    this.sseManager.addEventListener('order-update', (event) => {
      const data = JSON.parse(event.data);
      this.updateOrderCount(data.orders);
    });
    
    this.sseManager.addEventListener('revenue-update', (event) => {
      const data = JSON.parse(event.data);
      this.updateRevenue(data.revenue);
    });
    
    this.sseManager.addEventListener('alert', (event) => {
      const data = JSON.parse(event.data);
      this.addAlert(data);
    });
  }
  
  setupUI() {
    // Setup UI elements
    this.userCountElement = document.getElementById('userCount');
    this.orderCountElement = document.getElementById('orderCount');
    this.revenueElement = document.getElementById('revenue');
    this.alertsContainer = document.getElementById('alerts');
    this.connectionStatus = document.getElementById('connectionStatus');
  }
  
  handleDashboardUpdate(event) {
    try {
      const data = JSON.parse(event.data);
      
      switch (data.type) {
        case 'dashboard-update':
          this.updateDashboard(data.payload);
          break;
        case 'metric-update':
          this.updateMetric(data.metric, data.value);
          break;
        case 'alert':
          this.addAlert(data.alert);
          break;
      }
    } catch (error) {
      console.error('Error parsing dashboard update:', error);
    }
  }
  
  updateDashboard(payload) {
    this.data = { ...this.data, ...payload };
    this.renderDashboard();
  }
  
  updateMetric(metric, value) {
    this.data[metric] = value;
    this.updateMetricDisplay(metric, value);
  }
  
  updateUserCount(count) {
    this.data.users = count;
    this.userCountElement.textContent = count.toLocaleString();
    this.animateValueChange(this.userCountElement);
  }
  
  updateOrderCount(orders) {
    this.data.orders = orders;
    this.orderCountElement.textContent = orders.toLocaleString();
    this.animateValueChange(this.orderCountElement);
  }
  
  updateRevenue(revenue) {
    this.data.revenue = revenue;
    this.revenueElement.textContent = `$${revenue.toLocaleString()}`;
    this.animateValueChange(this.revenueElement);
  }
  
  addAlert(alert) {
    this.data.alerts.unshift(alert);
    
    // Keep only last 10 alerts
    if (this.data.alerts.length > 10) {
      this.data.alerts = this.data.alerts.slice(0, 10);
    }
    
    this.renderAlerts();
  }
  
  renderAlerts() {
    this.alertsContainer.innerHTML = '';
    
    this.data.alerts.forEach(alert => {
      const alertElement = document.createElement('div');
      alertElement.className = `alert alert-${alert.level}`;
      alertElement.innerHTML = `
        <div class="alert-content">
          <h4>${alert.title}</h4>
          <p>${alert.message}</p>
          <span class="alert-time">${new Date(alert.timestamp).toLocaleTimeString()}</span>
        </div>
        <button class="alert-close" onclick="this.parentElement.remove()">×</button>
      `;
      
      this.alertsContainer.appendChild(alertElement);
    });
  }
  
  updateConnectionStatus(status) {
    this.connectionStatus.textContent = status;
    this.connectionStatus.className = `status status-${status}`;
  }
  
  animateValueChange(element) {
    element.classList.add('value-updated');
    setTimeout(() => {
      element.classList.remove('value-updated');
    }, 1000);
  }
  
  startPeriodicUpdates() {
    // Update timestamps every minute
    setInterval(() => {
      this.updateTimestamps();
    }, 60000);
  }
  
  updateTimestamps() {
    const timestampElements = document.querySelectorAll('.timestamp');
    timestampElements.forEach(element => {
      const timestamp = new Date(element.dataset.timestamp);
      element.textContent = timestamp.toLocaleTimeString();
    });
  }
}

// Initialize dashboard
const dashboard = new RealTimeDashboard();

Live Notifications System​

Real-time Notification Manager​

class NotificationManager {
  constructor() {
    this.sseManager = null;
    this.notifications = [];
    this.maxNotifications = 50;
    this.notificationContainer = null;
    
    this.initialize();
  }
  
  async initialize() {
    this.setupUI();
    await this.setupSSE();
    this.setupNotificationHandlers();
  }
  
  setupUI() {
    this.notificationContainer = document.getElementById('notificationContainer');
    
    // Create notification bell icon
    const bellIcon = document.createElement('div');
    bellIcon.className = 'notification-bell';
    bellIcon.innerHTML = '🔔';
    bellIcon.addEventListener('click', () => {
      this.toggleNotificationPanel();
    });
    
    document.body.appendChild(bellIcon);
    
    // Create notification panel
    const panel = document.createElement('div');
    panel.id = 'notificationPanel';
    panel.className = 'notification-panel hidden';
    panel.innerHTML = `
      <div class="notification-header">
        <h3>Notifications</h3>
        <button class="clear-all" onclick="notificationManager.clearAll()">Clear All</button>
      </div>
      <div class="notification-list" id="notificationList"></div>
    `;
    
    document.body.appendChild(panel);
  }
  
  async setupSSE() {
    this.sseManager = new SSEManager('/api/notifications/stream');
    
    this.sseManager.on('open', () => {
      console.log('Notification stream connected');
    });
    
    this.sseManager.on('error', (error) => {
      console.error('Notification stream error:', error);
    });
    
    this.sseManager.on('message', (event) => {
      this.handleNotification(event);
    });
    
    // Handle specific notification types
    this.sseManager.addEventListener('user-notification', (event) => {
      const notification = JSON.parse(event.data);
      this.addNotification(notification);
    });
    
    this.sseManager.addEventListener('system-notification', (event) => {
      const notification = JSON.parse(event.data);
      this.addNotification(notification);
    });
    
    this.sseManager.addEventListener('alert-notification', (event) => {
      const notification = JSON.parse(event.data);
      this.addNotification(notification);
    });
  }
  
  setupNotificationHandlers() {
    // Handle browser notifications
    if ('Notification' in window) {
      Notification.requestPermission();
    }
    
    // Handle page visibility changes
    document.addEventListener('visibilitychange', () => {
      if (document.hidden) {
        this.pauseNotifications();
      } else {
        this.resumeNotifications();
      }
    });
  }
  
  handleNotification(event) {
    try {
      const notification = JSON.parse(event.data);
      this.addNotification(notification);
    } catch (error) {
      console.error('Error parsing notification:', error);
    }
  }
  
  addNotification(notification) {
    // Add to notifications array
    this.notifications.unshift({
      ...notification,
      id: Date.now(),
      timestamp: new Date(),
      read: false
    });
    
    // Keep only max notifications
    if (this.notifications.length > this.maxNotifications) {
      this.notifications = this.notifications.slice(0, this.maxNotifications);
    }
    
    // Display notification
    this.displayNotification(notification);
    
    // Show browser notification if permission granted
    this.showBrowserNotification(notification);
    
    // Update notification count
    this.updateNotificationCount();
  }
  
  displayNotification(notification) {
    const notificationElement = document.createElement('div');
    notificationElement.className = `notification-item ${notification.type}`;
    notificationElement.innerHTML = `
      <div class="notification-content">
        <div class="notification-icon">${this.getNotificationIcon(notification.type)}</div>
        <div class="notification-text">
          <h4>${notification.title}</h4>
          <p>${notification.message}</p>
          <span class="notification-time">${new Date().toLocaleTimeString()}</span>
        </div>
      </div>
      <button class="notification-close" onclick="this.parentElement.remove()">×</button>
    `;
    
    // Add click handler
    notificationElement.addEventListener('click', () => {
      this.handleNotificationClick(notification);
    });
    
    // Insert at the beginning of the list
    const notificationList = document.getElementById('notificationList');
    notificationList.insertBefore(notificationElement, notificationList.firstChild);
    
    // Auto-remove after 10 seconds
    setTimeout(() => {
      if (notificationElement.parentNode) {
        notificationElement.remove();
      }
    }, 10000);
  }
  
  showBrowserNotification(notification) {
    if ('Notification' in window && Notification.permission === 'granted') {
      const browserNotification = new Notification(notification.title, {
        body: notification.message,
        icon: '/icons/notification-icon.png',
        tag: notification.id
      });
      
      browserNotification.onclick = () => {
        this.handleNotificationClick(notification);
        browserNotification.close();
      };
      
      // Auto-close after 5 seconds
      setTimeout(() => {
        browserNotification.close();
      }, 5000);
    }
  }
  
  handleNotificationClick(notification) {
    // Mark as read
    const notificationItem = this.notifications.find(n => n.id === notification.id);
    if (notificationItem) {
      notificationItem.read = true;
    }
    
    // Handle notification action
    if (notification.action) {
      switch (notification.action.type) {
        case 'navigate':
          window.location.href = notification.action.url;
          break;
        case 'open-modal':
          this.openModal(notification.action.modalId);
          break;
        case 'execute-function':
          if (window[notification.action.functionName]) {
            window[notification.action.functionName](notification.action.params);
          }
          break;
      }
    }
    
    this.updateNotificationCount();
  }
  
  getNotificationIcon(type) {
    const icons = {
      'info': 'ℹ️',
      'success': '✅',
      'warning': '⚠️',
      'error': '❌',
      'user': '👤',
      'system': '⚙️',
      'alert': '🚨'
    };
    
    return icons[type] || '📢';
  }
  
  updateNotificationCount() {
    const unreadCount = this.notifications.filter(n => !n.read).length;
    const bellIcon = document.querySelector('.notification-bell');
    
    if (unreadCount > 0) {
      bellIcon.classList.add('has-notifications');
      bellIcon.setAttribute('data-count', unreadCount);
    } else {
      bellIcon.classList.remove('has-notifications');
      bellIcon.removeAttribute('data-count');
    }
  }
  
  toggleNotificationPanel() {
    const panel = document.getElementById('notificationPanel');
    panel.classList.toggle('hidden');
    
    if (!panel.classList.contains('hidden')) {
      this.renderNotificationList();
    }
  }
  
  renderNotificationList() {
    const notificationList = document.getElementById('notificationList');
    notificationList.innerHTML = '';
    
    this.notifications.forEach(notification => {
      const notificationElement = document.createElement('div');
      notificationElement.className = `notification-item ${notification.type} ${notification.read ? 'read' : 'unread'}`;
      notificationElement.innerHTML = `
        <div class="notification-content">
          <div class="notification-icon">${this.getNotificationIcon(notification.type)}</div>
          <div class="notification-text">
            <h4>${notification.title}</h4>
            <p>${notification.message}</p>
            <span class="notification-time">${notification.timestamp.toLocaleTimeString()}</span>
          </div>
        </div>
        <button class="notification-close" onclick="this.parentElement.remove()">×</button>
      `;
      
      notificationElement.addEventListener('click', () => {
        this.handleNotificationClick(notification);
      });
      
      notificationList.appendChild(notificationElement);
    });
  }
  
  clearAll() {
    this.notifications = [];
    this.renderNotificationList();
    this.updateNotificationCount();
  }
  
  pauseNotifications() {
    // Pause SSE connection when page is hidden
    if (this.sseManager) {
      this.sseManager.close();
    }
  }
  
  resumeNotifications() {
    // Resume SSE connection when page becomes visible
    if (this.sseManager) {
      this.sseManager.connect();
    }
  }
}

// Initialize notification manager
const notificationManager = new NotificationManager();

Performance Optimization​

Efficient SSE Handling​

class OptimizedSSE {
  constructor(url, options = {}) {
    this.url = url;
    this.options = {
      bufferSize: 100,
      flushInterval: 1000,
      ...options
    };
    
    this.eventSource = null;
    this.messageBuffer = [];
    this.flushTimer = null;
    this.messageHandlers = new Map();
    
    this.connect();
  }
  
  connect() {
    this.eventSource = new EventSource(this.url);
    this.setupEventHandlers();
  }
  
  setupEventHandlers() {
    this.eventSource.onmessage = (event) => {
      this.bufferMessage(event);
    };
    
    this.eventSource.onerror = (event) => {
      console.error('SSE error:', event);
    };
  }
  
  bufferMessage(event) {
    this.messageBuffer.push(event);
    
    // Flush buffer if it's full
    if (this.messageBuffer.length >= this.options.bufferSize) {
      this.flushBuffer();
    }
    
    // Schedule flush if not already scheduled
    if (!this.flushTimer) {
      this.flushTimer = setTimeout(() => {
        this.flushBuffer();
      }, this.options.flushInterval);
    }
  }
  
  flushBuffer() {
    if (this.messageBuffer.length === 0) {
      return;
    }
    
    // Process all buffered messages
    this.messageBuffer.forEach(event => {
      this.processMessage(event);
    });
    
    // Clear buffer
    this.messageBuffer = [];
    
    // Clear timer
    if (this.flushTimer) {
      clearTimeout(this.flushTimer);
      this.flushTimer = null;
    }
  }
  
  processMessage(event) {
    try {
      const data = JSON.parse(event.data);
      
      // Route to appropriate handler
      if (this.messageHandlers.has(data.type)) {
        const handler = this.messageHandlers.get(data.type);
        handler(data);
      } else {
        // Default handler
        console.log('Unhandled message type:', data.type);
      }
    } catch (error) {
      console.error('Error processing message:', error);
    }
  }
  
  onMessageType(type, handler) {
    this.messageHandlers.set(type, handler);
  }
  
  close() {
    if (this.flushTimer) {
      clearTimeout(this.flushTimer);
    }
    
    if (this.eventSource) {
      this.eventSource.close();
    }
  }
}

// Usage
const optimizedSSE = new OptimizedSSE('/api/events');

optimizedSSE.onMessageType('update', (data) => {
  updateUI(data);
});

optimizedSSE.onMessageType('notification', (data) => {
  showNotification(data);
});

Best Practices​

1. Error Handling and Reconnection​

// Good: Robust error handling
class RobustSSE {
  constructor(url) {
    this.url = url;
    this.eventSource = null;
    this.reconnectAttempts = 0;
    this.maxReconnectAttempts = 5;
    this.reconnectInterval = 3000;
  }
  
  connect() {
    try {
      this.eventSource = new EventSource(this.url);
      this.setupEventHandlers();
    } catch (error) {
      console.error('Failed to create EventSource:', error);
      this.handleReconnect();
    }
  }
  
  handleReconnect() {
    if (this.reconnectAttempts < this.maxReconnectAttempts) {
      this.reconnectAttempts++;
      setTimeout(() => {
        this.connect();
      }, this.reconnectInterval);
    } else {
      console.error('Max reconnection attempts reached');
    }
  }
  
  setupEventHandlers() {
    this.eventSource.onopen = () => {
      this.reconnectAttempts = 0;
    };
    
    this.eventSource.onerror = (event) => {
      if (this.eventSource.readyState === EventSource.CLOSED) {
        this.handleReconnect();
      }
    };
  }
}

// Avoid: No error handling
function badSSE(url) {
  const eventSource = new EventSource(url);
  // No error handling - bad practice
  return eventSource;
}

2. Resource Management​

// Good: Proper resource cleanup
class SSEResourceManager {
  constructor() {
    this.connections = [];
  }
  
  createConnection(url) {
    const eventSource = new EventSource(url);
    this.connections.push(eventSource);
    return eventSource;
  }
  
  closeAll() {
    this.connections.forEach(connection => {
      connection.close();
    });
    this.connections = [];
  }
  
  closeConnection(eventSource) {
    const index = this.connections.indexOf(eventSource);
    if (index > -1) {
      this.connections.splice(index, 1);
    }
    eventSource.close();
  }
}

// Avoid: Memory leaks
function badResourceManagement() {
  const eventSource = new EventSource('/api/events');
  // No cleanup - memory leak
}

3. Security Considerations​

// Good: Secure SSE implementation
class SecureSSE {
  constructor(url, options = {}) {
    this.url = url;
    this.options = {
      withCredentials: false,
      ...options
    };
    
    this.validateUrl();
    this.createSecureConnection();
  }
  
  validateUrl() {
    const url = new URL(this.url);
    if (url.protocol !== 'https:' && url.protocol !== 'http:') {
      throw new Error('Invalid protocol');
    }
  }
  
  createSecureConnection() {
    this.eventSource = new EventSource(this.url, {
      withCredentials: this.options.withCredentials
    });
  }
}

Summary​

Server-Sent Events are essential for real-time server-to-client communication:

  • EventSource API: Use for establishing SSE connections
  • Event Handling: Handle different event types and messages
  • Error Handling: Implement robust error handling and reconnection
  • Performance: Use buffering and optimization techniques
  • Security: Follow security best practices for SSE
  • Resource Management: Properly manage connections and cleanup
  • Real-time Applications: Build live dashboards, notifications, and updates

Mastering Server-Sent Events enables you to build responsive, real-time applications that provide excellent user experiences through instant server-to-client data push.

This tutorial is part of the JavaScript Mastery series by syscook.dev