Supported since NATS Server version 2.2
WebSocket support can be enabled in the server and may be used alongside the traditional TCP socket connections. TLS, compression and Origin Header checking are supported.
NATS Supports only WebSocket data frames in Binary, not Text format (https://tools.ietf.org/html/rfc6455#section-5.6). The server will always send in Binary and your clients MUST send in Binary too.
For writers of client libraries: a WebSocket frame is not guaranteed to contain a full NATS protocol (actually will generally not). Any data from a frame must be going through a parser that can handle partial protocols. See the protocol description here.