HTML | DOM onopen Event - GeeksforGeeks

The DOM onopen event occurs on an open connection with an event source.

Related events:

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

Syntax:

Using JavaScript:
```
object.onopen = function(){myScript};
```

Using the addEventListener() method:

object.addEventListener("open", myScript);

Example: Using the addEventListener() method

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

Output:

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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