A brief analysis of the implementation flaws of the beforeunload event in Firefox_javascript skills

beforeunload refers to the last opportunity for JS execution provided before the page is unloaded. As follows

Copy the code The code is as follows:

window.onbeforeunload = function() {
return 'The blog you are editing has not been saved. Are you sure you want to leave this page? ';
};

You can use the return value text to prompt the user. But this text is not displayed only in Firefox.
When refreshing the page, each browser behaves as follows

IE:

Chrome:

Firefox12:

Mozilla officials said that versions before Firefox 4 can modify the value through the returnValue of the event object, as follows

Copy code The code is as follows:

window.onbeforeunload = function(e) {
e = e || window.event;

// For IE and Firefox prior to version 4
if (e) {
e.returnValue = 'Any string';
}
return 'The blog you are editing has not been saved. Are you sure you want to leave this page? ';
};

Related:
https://developer.mozilla.org/en/DOM/window.onbeforeunload
https://bugzilla.mozilla.org/show_bug.cgi?id=588292