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HTML DOM onopen Event

Last Updated : 15 Jun, 2023
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The DOM onopen event occurs on an open connection with an event source. 

Related events:

  • onmessage: Received the message.
  • onerror: The problem occurs.


  • Using JavaScript:
object.onopen = function(){myScript};
  • Using the addEventListener() method:
object.addEventListener("open", myScript); 

Example: Using the addEventListener() method 


<!DOCTYPE html>
        HTML DOM onopen Event
    <h1 id="gfg"></h1>
    <div id="geeks"></div>
        if (typeof (EventSource) !== "undefined") {
            let source = new EventSource("/html/demo_sse.php");
            source.addEventListener("open", function () {
                document.getElementById("gfg").innerHTML =
            source.addEventListener("message", function (event) {
                document.getElementById("geeks").innerHTML +=
           + "<br>";
        } else {
            document.getElementById("gfg").innerHTML =
                "Browser does not support";



Supported Browsers: The browsers supported by HTML DOM onopen Event are listed below:

  • Google Chrome 9.0
  • Firefox 6.0
  • Apple Safari 5.0
  • Opera 11.0

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