Aw Qirui Guo Aw Qirui Guo - 1 year ago 248
Javascript Question

How to customize the message "Changes you made may not be saved." for window.onbeforeunload?

I am testing in Google Chrome.

I did some search and found that someone is using:

window.onbeforeunload = function() {
if (hook) {
return "Did you save your stuff?"

But when I use it, I still got the "Changes you made may not be saved." message. How can I change it to something I want?


Answer Source

You can't, the ability to do this was removed in Chrome 51. It is widely considered a security issue, and most vendors have removed support.

Custom messages in onbeforeunload dialogs (removed):

A window’s onbeforeunload property may be set to a function that returns a string. If the function returns a string, then before unloading the page, a dialog is shown to have the user confirm that they indeed want to navigate away. The string provided by the function will no longer be shown in the dialog. Rather, a generic string not under the control of the webpage will be shown.


This shipped in Safari 9.1, and has been shipping in Firefox since Firefox 4. Safari considers this a security fix and assigned it CVE-2009-2197 (see ). Approved with the intent .


Established standard

Status in Chromium

Removed (launch bug) in:

  • Chrome for desktop release 51
  • Chrome for Android release 51
  • Android WebView release 51
  • Opera release 38
  • Opera for Android release 38
Recommended from our users: Dynamic Network Monitoring from WhatsUp Gold from IPSwitch. Free Download