onbeforeunload
Event
Example
Execute JavaScript when leaving the current page (refresh or close):
<body onbeforeunload="return myFunction()">
Definition and Usage
The onbeforeunload
event is triggered when the page is about to be unloaded (refresh or close).
This event can be used to display a dialog box asking the user whether to stay on the page or leave.
The default message in the dialog box varies by browser, typically something like "Are you sure you want to leave this page?". This default message cannot be removed.
However, you can customize additional messages to be displayed alongside the default message.
Note: If you do not specify the onbeforeunload
event on the <body>
element, you need to add the event to the window
object and use the returnValue
property to create a custom message (see the syntax example below).
Note: In Firefox, only the default alert message is displayed (custom messages are not shown).
Browser Support
The numbers in the table indicate the first browser version that supports the event.
Event | |||||
---|---|---|---|---|---|
onbeforeunload | Yes | Yes | Yes | Yes | 15.0 |
Syntax
In HTML:
In JavaScript:
In JavaScript, using the addEventListener()
method:
Note: Internet Explorer 8 and earlier versions do not support the addEventListener()
method.
Bubbles: | No |
---|---|
Cancelable: | Yes |
--- | --- |
Event Type: | Event |
--- | --- |
Supported HTML Tags: | <body> |
--- | --- |