Example
Execute a JavaScript when the page is about to be unloaded:
<body onbeforeunload="return myFunction()">
Try it Yourself »
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.
| Event Attribute | |||||
|---|---|---|---|---|---|
| onbeforeunload | Yes | Yes | Yes | Yes | 15.0 |
Differences Between HTML 4.01 and HTML5
None.
Syntax
<element onbeforeunload="script">
Attribute Values
| Value | Description |
|---|---|
| script | The script to be run on onbeforeunload |
Technical Details
| Supported HTML tags: | <body> |
|---|
Related Pages
HTML DOM reference: onbeforeunload event