clear websocket attribute without waiting for previous websocket to finish closing

which may never finish

Author: minrk

notebook/static/services/kernels/kernel.js

@@ -576,18 +576,13 @@ define([
          *
          * @function stop_channels
          */
-        var that = this;
-        var close = function () {
-            if (that.ws && that.ws.readyState === WebSocket.CLOSED) {
-                that.ws = null;
-            }
-        };
         if (this.ws !== null) {
-            if (this.ws.readyState === WebSocket.OPEN) {
-                this.ws.onclose = close;
-                this.ws.close();
-            } else {
-                close();
+            var ws = this.ws;
+            this.ws = null;
+            if (ws.readyState === WebSocket.OPEN) {
+                // unregister onclose callbacks
+                ws.onclose = function () {};
+                ws.close();
             }
         }
     };