Hi "Peace Be Upon You", <br /> concerning 'onmessage in Server Side Events', i had the same problem too, But i found out that problem is with Server side code not client. <br /> Take a look at this simple demo i have made:<br /> https://github.com/n4j1Br4ch1D/onmessage-in-Server-Side-Events-is-not-working <br /> I hope it solves Your Problem.