HTML | onbeforeunload Event Attribute

The onbeforeunload event run when the document is about to be unloaded. This event is used to allow to display a message in a dialog box to inform the user to he/she wants to stay or leave the current page.

Syntax:

<element onbeforeunload = "script">

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

Example:

<!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>    
        <a href="https://www.geeksforgeeks.org">Go to GeeksforGeeks</a> 
        <script> 
        function myFunction() { 
            return "This document is ready to load"; 
        } 
        </script> 
    </body> 
</html> 

Output:

Supported Browsers: The browser supported by onbeforeunload attribute are listed below:

Google Chrome
Internet Explorer
Firefox
Safari
Opera 15.0 and above

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