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HTML onbeforeunload Event Attribute

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The onbeforeunload event runs when the document is about to be unloaded, thus, allowing to display message in a dialog box to inform the user whether a user wants to stay or leave the current page, i.e., this event triggers just before a user leaves a webpage, and helps to prevent an accidental closures and retaining unsaved changes. The message rendered will be different for different browsers.

Supported Tags 

Syntax

<element onbeforeunload = "script">

Attribute Value

This attribute contains a single value script and it runs when onbeforeunload event is called. This event attribute is supported by <body> tag.

Example: In this example, we will implement the HTML onbeforeunload Event Attribute to trigger the alert message.

html

<!DOCTYPE html>
<html>
 
<head>
    <title>onbeforeunload attribute</title>
    <style>
        body {
            text-align: center;
        }
 
        h1 {
            color: green;
        }
 
        a {
            text-decoration: none;
            font-weight: bold;
        }
    </style>
</head>
 
<body onbeforeunload="return myFunction()">
    <h1>
        GeeksforGeeks
    </h1>
    <h2>
        onbeforeunload attribute
    </h2>
        Go to GeeksforGeeks
    </a>
    <script>
        function myFunction() {
            return "This document is ready to load";
        }
    </script>
</body>
 
</html>

                    

Output:

qw

Supported Browsers

The browser supported by onbeforeunload attribute are listed below: 

  • Google Chrome 1 and above
  • Edge 12 and above
  • Firefox 1 and above
  • Opera 15 and above
  • Safari 3 and above


Last Updated : 13 Dec, 2023
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