SockJS-client

<script src="https://cdn.jsdelivr.net/npm/sockjs-client@1/dist/sockjs.min.js"></script>

const SockJS = require('sockjs-client');

import SockJS from 'sockjs-client';

// Create connection
const sock = new SockJS('https://mydomain.com/my_prefix');

// Set up event handlers
sock.onopen = function() {
    console.log('Connected');
    sock.send('Hello Server!');
};

sock.onmessage = function(e) {
    console.log('Received:', e.data);
};

sock.onclose = function() {
    console.log('Disconnected');
};

sock.onerror = function() {
    console.log('Connection error');
};

// Later: close connection
sock.close();

/**
 * SockJS constructor - creates a new SockJS connection
 * @param {string} url - Connection URL (http/https), may contain query string
 * @param {string|string[]} [protocols] - Protocols (reserved parameter, typically not used)
 * @param {object} [options] - Configuration options
 */
function SockJS(url, protocols, options);

// Instance properties
SockJS.prototype.url;           // string - Connection URL
SockJS.prototype.readyState;    // number - Current connection state (0-3)
SockJS.prototype.extensions;    // string - Always empty string
SockJS.prototype.protocol;      // string - Always empty string  
SockJS.prototype.transport;     // string - Active transport name when connected

// Instance methods
SockJS.prototype.send(data);           // Send data (converts non-strings to strings)
SockJS.prototype.close(code, reason);  // Close connection with optional code and reason

// Static constants
SockJS.CONNECTING;  // 0 - Connection being established
SockJS.OPEN;        // 1 - Connection is open
SockJS.CLOSING;     // 2 - Connection is closing  
SockJS.CLOSED;      // 3 - Connection is closed

// Static property
SockJS.version;     // string - Library version

// Event handler properties
sock.onopen = function() { /* connection opened */ };
sock.onmessage = function(e) { /* message received: e.data */ };
sock.onclose = function(e) { /* connection closed: e.code, e.reason, e.wasClean */ };
sock.onerror = function() { /* connection error */ };

// EventTarget methods
sock.addEventListener(type, listener);    // Add event listener
sock.removeEventListener(type, listener); // Remove event listener
sock.dispatchEvent(event);               // Dispatch event

// Constructor options for transport configuration
const options = {
  server: string,           // Server identifier (default: random 4-digit number)
  transports: string|Array, // Whitelist of allowed transports
  sessionId: number|function, // Session ID generation (default: 8 chars)
  timeout: number,          // Minimum timeout for transport connections
  transportOptions: object  // Transport-specific configuration
};

// Available transport names for whitelisting
const availableTransports = [
  'websocket',
  'xhr-streaming', 
  'xdr-streaming',
  'eventsource',
  'iframe-eventsource',
  'htmlfile',
  'iframe-htmlfile', 
  'xhr-polling',
  'xdr-polling',
  'iframe-xhr-polling',
  'jsonp-polling'
];

// Options interface for SockJS constructor
interface SockJSOptions {
  server?: string;                    // Server identifier
  transports?: string | string[];     // Transport whitelist
  sessionId?: number | (() => string); // Session ID configuration
  timeout?: number;                   // Connection timeout
  transportOptions?: object;          // Transport-specific options
}

// Event objects
interface SockJSMessageEvent {
  type: 'message';
  data: any;    // Message payload
}

interface SockJSCloseEvent {
  type: 'close';
  code: number;      // Close code
  reason: string;    // Close reason
  wasClean: boolean; // Clean close flag
}

interface SockJSEvent {
  type: 'open' | 'error' | 'heartbeat';
}