how to subscribe from server (javascript, html, python, ajax)

EventSource, stream.onmessage, Response()

javascript side

    var stream = new EventSource('/api/stream');
    stream.onmessage = function(e) {
      console.info(e.data);
      $("#received").append(e.data+"\n");
      $("#received")[0].scrollTop = $("#received")[0].scrollHeight;
    };



python side
#from queue import Queue
#from flask import Response
queue = Queue()
def event_stream():
    while True:
     # Question: how to break out of this loop when the app is killed?
        message = queue.get(True)
        print("Sending {}".format(message))
        yield "data: {}\n\n".format(message)


@app.route('/api/stream')
def stream():
    return Response(event_stream(), mimetype="text/event-stream")

reference 

https://www.w3schools.com/html/html5_serversentevents.asp