[Chapter 21] Reference: Window.onunload()
Author: David Flanagan
Date: Fri Aug 29 11:21:23 1997

#

| Chapter 21 JavaScript Reference |

# Window.onunload() Handler

## Name

Window.onunload() Handler---executed when the browser leaves a page

## Availability

Navigator 2.0, Internet Explorer 3.0

## Synopsis

    <BODY    a definition of the handler
        [ onUnload="JavaScript statements" ]
            ...
    >
    <FRAMESET    another way to define the handler
        [ onUnload="JavaScript statements" ]
           ...
    >
    window.onunload=handler-func    defining the handler directly
    window.onunload();    an explicit invocation of the handler

## Description

`onunload()` is an event handler invoked by the browser when it unloads (i.e., leaves) a document or a frameset. The `onunload()` handler is defined by the `onUnload` attribute of the `<BODY>` or `<FRAMESET>` HTML tags. The value of this attribute may be any number of JavaScript statements, separated by semicolons.

The `onunload()` event handler provides the opportunity to perform any necessary "clean-up" of the browser state before a new document is loaded. For example, an `onunload()` handler might restore the `Window.defaultStatus` property (the default message in the status line) to the empty string.

When the browser leaves a site using frames, the `onunload()` handlers for each frame will be invoked before the `onunload()` handler of the browser itself.

## Usage

The `onunload()` handler is invoked when the user has instructed the browser to leave the current page and move somewhere else. Therefore, it is almost never appropriate to delay the loading of the desired new page by popping up dialog boxes (with `Window.confirm()` or `Window.prompt()` for example) from an `onunload()` event handler.

## See Also

"Window", "Window.onunload()"

Window.onload() |  | Window.open()