Passing Variable to Websockets in VUE.js

I'm starting to use VUE + Websockets, I'm using Ratchet.

I need to pass a variable to my server.php file (WS execution file),

My front looks like this:

var self = this;
self.ws = new WebSocket('ws://localhost:9000');

self.ws.onopen = function( this.user ) {
self.addSuccessNotification('Conectado' + self.user);
// Se houver método de retorno
if (onOpen) {
onOpen(this.user);
}

I would like to pass a value with the user code registered in my system, how should I proceed?