It's very common to invoke SSE services from JavaScript code in a browser to update the page as the keep coming from the service. Most modern browsers support the SSE protocol and provide the EventSource object, which makes invoking an SSE service very simple.

To invoke our forecast service, we only need the following code:

var source = new EventSource("http://localhost:8080/forecast-service-async/" +
   "smartcity/forecast");
source.onmessage = function (event) {
   if (event.lastEventId === "completed") {
      source.close();
   } else {
      alert("Received: " + event.data);
   }
};

• Create an instance of the EventSource object and immediately open a connection to the SSE service.
• Provide a function to handle messages as the onmessage property of our EventSource instance.
• The handler validates the value of lastEventId to detect the final message, and closes the EventSource object when the final message is received.