I'm testing some performance things on the client with lighthouse and found that there was still a window.unload listener which is really bad for perf and disabled bf-caching.

I found that SockJS adds this listener: https://github.com/meteor/meteor/blob/devel/packages/socket-stream-client/sockjs-0.3.4.js#L648

However, SockJs should never be loaded to my app, because it's marked as legacy in package.js: https://github.com/meteor/meteor/blob/devel/packages/socket-stream-client/package.js#L18

Repro:

• create new Meteor Project (my current release is METEOR@2.7.3)
• run meteor --production --exclude-archs "web.browser.legacy"
• open source code and search for sockjs you will find it as part of socket-stream-client
• Meteor.connection._stream.socket gives

{
	  onclose: ()=>{this._lostConnection()}
	  onerror: e=> {…}
	  onheartbeat: ()=>{this.lastError=null,this._heartbeat_received()}
	  onmessage: e=> {…}
	  onopen: e=>{this.lastError=null,this._connected()}
	  protocol: "websocket"
	  readyState: 1
	  _base_url: "http://localhost:3000/sockjs"
	  _ir: null
	  _options: {devel: false, debug: false, protocols_whitelist: Array(5), info: {…}, rtt: 23, …}
	  _protocols: ['xhr-polling']
	  _server: "014"
	  _transport: k.websocket {ri: k, url: 'ws://localhost:3000/sockjs/014/decfbp0y/websocket', ws: WebSocket, unload_ref: '0fyje_kk'}
	  _transport_tref: null
}

My assumption is that is line: https://github.com/meteor/meteor/blob/devel/packages/socket-stream-client/browser.js#L11

The import may still cause sockjs to be bundled. If so wouldn't this also mean that all clients forcefully use sockjs, even if they are modern architecure?

Can anyone confirm this issue or give me some insight on this?