SockJS-client is a browser JavaScript library that provides WebSocket emulation for real-time communication between browsers and web servers.
SockJS solves the problem of establishing reliable, low-latency bidirectional communication in environments where native WebSockets are unavailable or blocked. It presents a unified API that closely follows the HTML5 WebSocket standard while automatically falling back to alternative transport protocols when needed. The library attempts to use native WebSockets first, then tries streaming protocols like Server-Sent Events or long-polling depending on browser capabilities and network constraints. This approach ensures cross-domain communication works out of the box and functions behind restrictive corporate proxies without requiring Flash or other plugins.
Developers should choose SockJS-client when building real-time applications that must support older browsers or operate in restricted network environments where WebSocket support cannot be guaranteed. It suits projects requiring a consistent API across diverse browser versions and network configurations. The library requires a corresponding server implementation; SockJS-node provides the server counterpart for Node.js environments. The design philosophy prioritizes fast connection establishment, cross-domain support with cookie handling for sticky sessions, and compatibility with all major browsers through at least one streaming protocol per browser family.
The project maintains active engagement with its user community through a dedicated mailing list for discussions and support. Commercial support and maintenance are available through a subscription service that includes the maintainers' involvement. The codebase is deployed and monitored through continuous integration infrastructure.
