ESP8266 Community Forum

Posted: **Mon Dec 13, 2021 12:10 pm**

I tried to build a system that send data, like a simple status on/off, from ESP8266 to a webpage via ESP8266WebServer methods.

At the ESP8266 side I had a function named "handleUpdateData" that I used both in server handler declaration with this declaration

Code: Select allserver->on("/updatedata", handleUpdateData);

and called asynchronously when i got some variation of the status that i would to be check.

In the "handleUpdateData" function i builded the JSON string with "page" variable using the data stream syntax like

Code: Select all

id: 12345
data: { "code": "123",
data: "status": "xxxx" }

and sended it by this instruction

Code: Select allserver->send(200, "text/event-stream", page);

At the webpage side i had this declaration in javascript first

Code: Select allvar eventSource = new EventSource("/updatedata");

and after that with

Code: Select all

eventSource.onmessage = function(e) {
  debug("onmessage: "+e.data);
 }

OR (without differences)

Code: Select all

eventSource.addEventListener("message", function(e) {
  debug("received message: "+e.data);
 }

In both cases, i received data every 5 seconds regulary.

In case of some exception, when ESP8266 side i builded a new send, at the webpage side I had nothing out synch of 5 seconds, despite i used the id in the message frame that was not verified by web browser.

What's wrong?

ESP8266 Community Forum

how can send data from ESP8266 to client in "real" real-time

how can send data from ESP8266 to client in "real" real-time