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uws tries to mimic ws as closely as possible without sacrificing too much performance. In most cases you simply swap require('ws') with require('uws'):

var WebSocketServer = require('uws').Server;
var wss = new WebSocketServer({ port: 3000 });
function onMessage(message) {
    console.log('received: ' + message);
wss.on('connection', function(ws) {
    ws.on('message', onMessage);
Deviations from ws

There are some important incompatibilities with ws though, we aim to be ~90% compatible but will never implement behavior that is deemed too inefficient:

  • Binary data is passed zero-copy as an ArrayBuffer. This means you need to copy it to keep it past the callback. It also means you need to convert it with Buffer.from(message) if you expect a Node.js Buffer.
  • webSocket._socket is not a net.Socket, it is just a getter function with very basic functionalities.
  • webSocket._socket.remote... might fail, you need to cache it at connection.
  • webSocket acts like an EventEmitter with one listener per event maximum.
  • webSocket.upgradeReq is only valid during execution of the connection handler. If you want to keep properties of the upgradeReq for the entire lifetime of the webSocket you better attach that specific property to the webSocket at connection.


At installation uws will try to recompile itself using the system's C++11 compiler (GCC 4.8+, Clang 3.3, VC++ 2015+). If this fails it will silently fall back to using the precompiled binaries. NPM installation will never fail but require('uws') will throw if it cannot properly load the binary module.