When profiling my Meteor+React app in Chrome Dev Tools I notice a number of long running (~500ms) function calls from sockjs-0.3.4.js. From the profiling stack trace it seems to me that these function calls are triggered by websocket messages (judging from “that.ws.onmessage”). However, if I try to set a breakpoint on line 6 in PatientActions (see screenshot below) Chrome Dev Tools (v53.0.2785.116 64-bit) never pauses at this breakpoint. Printing debug info using console.log(…) in this file does not help either as the debug info never is printed to the browsers console.
What is going on here? Are the websocket messages dispatched on a separate thread (WebWorker?) that is not connected to the browsers console and debugger? How do I go about debugging this? Thanks! 