support websocket protocol, this is optional option.

src/Main.js

@@ -3,10 +3,10 @@ import Emitter from './Emitter'
 
 export default {
 
-  install (Vue, connection, store, opts = {}) {
+  install (Vue, connection, protocol = '', store, opts = {}) {
     if (!connection) { throw new Error('[vue-native-socket] cannot locate connection') }
 
-    let observer = new Observer(connection, store, opts)
+    let observer = new Observer(connection, store, protocol, opts)
 
     Vue.prototype.$socket = observer.WebSocket
 

src/Observer.js

@@ -1,15 +1,15 @@
 import Emitter from './Emitter'
 
 export default class {
-  constructor (connectionUrl, store, opts = {}) {
+  constructor (connectionUrl, protocol, store, opts = {}) {
     this.format = opts.format && opts.format.toLowerCase()
-    this.connect(connectionUrl)
+    this.connect(connectionUrl, protocol)
     if (store) { this.store = store }
     this.onEvent()
   }
 
-  connect (connectionUrl) {
-    this.WebSocket = new WebSocket(connectionUrl)
+  connect (connectionUrl, protocol) {
+    this.WebSocket = new WebSocket(connectionUrl, protocol)
     if (this.format === 'json') {
       if (!('sendObj' in this.WebSocket)) {
         this.WebSocket.sendObj = (obj) => this.WebSocket.send(JSON.stringify(obj))