Possibility to disable JSONP. Emitting an error if JSONP is the only available transport.

lib/socket.js

@@ -71,6 +71,7 @@ function Socket(uri, opts){
   this.upgrade = false !== opts.upgrade;
   this.path = (opts.path || '/engine.io').replace(/\/$/, '') + '/';
   this.forceJSONP = !!opts.forceJSONP;
+  this.noJSONP = !!opts.noJSONP;
   this.forceBase64 = !!opts.forceBase64;
   this.timestampParam = opts.timestampParam || 't';
   this.timestampRequests = opts.timestampRequests;
@@ -140,6 +141,7 @@ Socket.prototype.createTransport = function (name) {
     path: this.path,
     query: query,
     forceJSONP: this.forceJSONP,
+    noJSONP: this.noJSONP,
     forceBase64: this.forceBase64,
     timestampRequests: this.timestampRequests,
     timestampParam: this.timestampParam,
@@ -169,11 +171,26 @@ Socket.prototype.open = function () {
   var transport;
   if (this.rememberUpgrade && Socket.priorWebsocketSuccess && this.transports.indexOf('websocket') != -1) {
     transport = 'websocket';
+  } else if (0 == this.transports.length) {
+    // Emit error on next tick so it can be listened to
+    var self = this;
+    setTimeout(function() {
+      self.emit('error', 'No transports available');
+    }, 0);
+    return;
   } else {
     transport = this.transports[0];
   }
   this.readyState = 'opening';
   var transport = this.createTransport(transport);
+
+  // If polling and JSONP disabled (constructor returns null)
+  if (!transport.name) {
+    this.transports.shift();
+    this.open();
+    return;
+  }
+
   transport.open();
   this.setTransport(transport);
 };

lib/transports/index.js

@@ -43,6 +43,6 @@ function polling(opts){
   if ('open' in xhr && !opts.forceJSONP) {
     return new XHR(opts);
   } else {
-    return new JSONP(opts);
+    return opts.noJSONP ? null : new JSONP(opts);
   }
 }