onbeforeunload HTML Attribute

The "onbeforeunload" attribute in HTML is an event attribute which can be added to an element, that when triggered, runs a script before the user leaves the current page. This attribute can be used to prompt the user with a message asking if they are sure they want to leave the page, or to save the user's data before they leave. The attribute value is a string containing the JavaScript code that should be executed when the event is fired, and it can also contain a message that will be displayed to the user in the dialog box.

For example, in the following code snippet, the onbeforeunload attribute is used to prompt the user with a message asking if they are sure they want to leave the page:


<body onbeforeunload="return 'Are you sure you want to leave this page?'">

It's worth noting that the onbeforeunload attribute is supported by most modern browsers, but it's usage is considered bad practice because it can be intrusive and annoying for the user, and it's also considered a security risk because it can be used for phishing attempts, for this reason, it's not recommended to use it unless it's strictly necessary and it's used in a responsible way.

In summary, the "onbeforeunload" attribute in HTML is an event attribute which can be added to an element, that when triggered, runs a script before the user leaves the current page. It can be used to prompt the user with a message asking if they are sure they want to leave the page, or to save the user's data before they leave. It's supported by most modern browsers, but it's usage is considered bad practice because it can be intrusive and annoying for the user, and it's also considered a security risk because it can be used for phishing attempts, it's not recommended to use it unless it's strictly necessary and it's used in a responsible way.