HTML onbeforeunload Event Attribute - Window Event Attributes

Definition and Usage

The onbeforeunload event fires when the document is about to be unloaded.

This event allows you to display a message in a confirmation dialog box to inform the user whether he/she wants to stay or leave the current page.

The default message that appears in the confirmation box, is different in different browsers. However, the standard message is something like "Are you sure you want to leave this page?". You cannot remove this message.

However, you can write a custom message together with the default message. See the first example on this page.

Note: In Firefox, only the default message will be displayed (not the custom message (if any)).

Browser Support

The numbers in the table specify the first browser version that fully supports the event.

Syntax

<element onbeforeunload="script">

Attribute Values

Value	Description
script	The script to be run on onbeforeunload

Technical Details

Supported HTML tags:	<body>

Example of HTML onbeforeunload Event

Here executes a JavaScript when the page is about to be unloaded.

index.html

Example: HTML

<!DOCTYPE html>
<html>
<body onbeforeunload="return myFunction()">

<p>Close this window, press F5 or click on the link below to invoke the onbeforeunload event.</p>

<a href="https://horje.com">Click here to go to horje.com</a>
  
<script>
function myFunction() {
  return "Write something clever here...";
}
</script>

</body>
</html>

Output should be:

How to execute a JavaScript when the page is about to be unloaded

Close this window, press F5 or click on the link below to invoke the onbeforeunload event.

index.html

Example: HTML

<!DOCTYPE html>
<html>
<body onbeforeunload="return myFunction()">

<p>Close this window, press F5 or click on the link below to invoke the onbeforeunload event.</p>

<a href="https://horje.com">Click here to go to horje.com</a>
  
<script>
function myFunction() {
  return "Write something clever here...";
}
</script>

</body>
</html>

Output should be:

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Single Articles

How to execute a JavaScript when the page is about to be unloaded

Window Event Attributes

Type:	Develop
Category:	Web Tutorial
Sub Category:	Window Event Attributes
Uploaded by:	Admin

Reffered: https://www.w3schools.com/tags/ev_onbeforeunload.asp