Yawl is a Node.js module which provides an API to create a web socket server and a web socket client. It is RFC 6455 compliant with two exceptions:

First, it uses Node.js's built in UTF-8 decoding instead of strictly closing the connection when decoding errors occur.

Second, the "payload length" field is limited to 2 to the power of 52 instead of 2 to the power of 64.

yawl uses streams and handles backpressure correctly. It is a pure JavaScript implementation.

Node.js is an event-based server-side JavaScript engine.