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How can I detect back button in the browser?

I have a function named back() which will be used for ajax calls. Actually I have an array stack contains last 5 search results and that back function will switch to the previous result set (according to that array stack) and it even changes the URL using window.history.pushState() when you click on the back button.
That back button I was talking about, is an element inside the browser which revokes back() function. Now I want to revoke back() function also when user click on the back button of the browser. Something like this:
window.onhashchange = function() {
back(); // this function also changes the url
}
But sadly window.onhashchange will be revokes twice when I click on the back of the browser. Because window.onhashchange will be revoked when you change the URL using window.history.pushState().
Anyway, how can I detect what things changes the URL? Either my JS code or the back button of the browser?

You can use performance.navigation.type
At any given point, for example on document.onload, you can read the value of type and, if it's:
0 The page was accessed by following a link, a bookmark, a form submission, a script, or typing the URL in the address bar.
1 The page was accessed by clicking the Reload button or via the Location.reload() method.
2 The page was accessed by navigating into the history.
255 any other way.
Just beware that support is limited according to the compatibilty table.
However, from the looks of it, it seems the table is outdated. It says it is not supported on chrome and I just tested it and works as expected on my chrome version (67.0)

One of solution is to implement onunload event with localstorage option.
This is from my head maybe you will need correction but this is base !
var history = [];
window.onload = function(){
var handler;
if ( localStorage.getItem('history') == null ) {
// FIRST TIME
history[0] = window.location.href;
localStorage.setItem("history", JSON.stringify(history));
}
else {
handler = localStorage.getItem('history');
handler = JSON.parse(handler);
history = handler;
// Just compare now
if (history[history.length-1] == window.location.href) {
// no change
} else {
history.push(window.location.href);
}
}
}
window.onunload = function(){
localStorage.setItem('history', JSON.stringify(history));
}
Note :
Since 25 May 2011, the HTML5 specification states that calls to
window.alert(), window.confirm(), and window.prompt() methods may be
ignored during this event. See the HTML5 specification for more
details.

Prevent XUL notificationBox from closing when button is hit

I have a problem concerning the notificationBox. I create a notification using
appendNotification( label , value , image , priority , buttons, eventCallback )
and supply a button in the buttons argument.
Now, I want to prevent the notificationBox from closing when I hit the button. The XUL Documentation states that this can be done by throwing an error in the eventCallback function:
This callback can be used to prevent the notification box from closing on button click. In the callback function just throw an error. (For example: throw new Error('prevent nb close');)
This does not work for me, however, it works when I add the throw-statement to the callback function of the button itself.
Is this a bug in XUL or an inconsistency with the documentation?
Is there any harm done by adding it to the button's callback function?

In my opinion, this is an error in the documentation not a bug in the code. However, throwing an error in your button callback to prevent closure is not the best way to accomplish that goal.
Looking at the source code, there were clearly multiple discrepancies between the code and the documentation regarding how buttons work on a notification.
There is a specifically coded method of preventing the notification closing from within the button callback (return true from the callback).
Throwing an error in order to accomplish a normal functionality is usually a bad programming practice. Doing so also results in an error showing in the console every time your button is pressed. Having errors intentionally showing in the console under normal operation is bad. It also can result in your add-on not being approved in review.
As it was documented (not as operational), if you wanted to close when one button was pressed and not close when another was pressed, you would have to store in a global variable which button callback was last called and then choose based on that information if you wanted to prevent closure when your notificationBox callback was executed. That would be an inappropriately complex way to design operation of these notification buttons.
Given all that, I would say that intentionally throwing an error in order to prevent closure is not the "correct" way to do it. While, trowing an error to prevent closure doesn't cause any harm to the operation of the notification box, it does show the error in the console, which is bad.
The correct way to prevent the notification from closing from within the notification button callback is to return a True value from the callback.
While it is possible that the previously inaccurately documented way of doing this the way they intended to have it operate, it is not the way it actually works. Given
It is easier to update the documentation than it is to make changes to the code.
The code works in a way that is better than the documented method.
There were other inaccuracies in the documentation that would have prevented people from using functionality which was supposedly working (popups/menu buttons).
I have, therefore, updated the documentation to reflect what is actually in the source code and copied, with some modification, the code from this answer to an example there.
Here is some code I used to test this:
function testNotificationBoxWithButtons() {
//Create some common variables if they do not exist.
// This should work from any Firefox context.
// Depending on the context in which the function is being run,
// this could be simplified.
if (typeof window === "undefined") {
//If there is no window defined, get the most recent.
var window=Components.classes["#mozilla.org/appshell/window-mediator;1"]
.getService(Components.interfaces.nsIWindowMediator)
.getMostRecentWindow("navigator:browser");
}
if (typeof gBrowser === "undefined") {
//If there is no gBrowser defined, get it
var gBrowser = window.gBrowser;
}
function testNotificationButton1Callback(theNotification, buttonInfo, eventTarget) {
window.alert("Button 1 pressed");
//Prevent notification from closing:
//throw new Error('prevent nb close');
return true;
};
function testNotificationButton2Callback(theNotification, buttonInfo, eventTarget) {
window.alert("Button 2 pressed");
//Do not prevent notification from closing:
};
function testNotificationCallback(reason) {
window.alert("Reason is: " + reason);
//Supposedly prevent notification from closing:
//throw new Error('prevent nb close');
// Does not work.
};
let notifyBox = gBrowser.getNotificationBox();
let buttons = [];
let button1 = {
isDefault: false,
accessKey: "1",
label: "Button 1",
callback: testNotificationButton1Callback,
type: "", // If a popup, then must be: "menu-button" or "menu".
popup: null
};
buttons.push(button1);
let button2 = {
isDefault: true,
accessKey: "2",
label: "Button 2",
callback: testNotificationButton2Callback,
type: "", // If a popup, then must be: "menu-button" or "menu".
popup: null
};
buttons.push(button2);
//appendNotification( label , value , image (URL) , priority , buttons, eventCallback )
notifyBox.appendNotification("My Notification text", "Test notification unique ID",
"chrome://browser/content/aboutRobots-icon.png",
notifyBox.PRIORITY_INFO_HIGH, buttons,
testNotificationCallback);
}

Return a value from window.open

We recently discovered that Chrome no longer supports window.showModalDialog which is problematic because our enterprise application uses this method.
There is, apparently, a short term workaround that allows you to restore showModalDialog but it involves modifying the registry which is too complicated (and risky) four our average user. Therefore I'm not a big fan of this workaround.
The long term solution is obviously to remove all calls to this obsolete method and replace them with a convenient jQuery plugin (such as VistaPrint's Skinny Modal Dialog plugin, for example. Other suggestions are welcome by the way).
The typical scenario we use the modal dialog is to ask the user for Yes/No confirmation before executing an action that cannot be undone, ask the user to agree to terms and condition before proceeding, etc. Typically the onclick event on the "Yes" or "Ok" button in the modal dialog looks like this:
window.returnValue = true;
window.close();
Similarly, the "Cancel" or "No" button looks like this:
window.returnValue = false;
window.close();
The fact that we can return a value from the dialog is very convenient because it allows the "parent" window to be notified whether the user has clicked the "Ok" or the "Cancel" button like so:
var options = "center:1;status:1;menubar:0;toolbar:0;dialogWidth:875px;dialogHeight:650px";
var termsOfServiceAccepted = window.showModalDialog(myUrl, null, options);
if (termsOfServiceAccepted) {
... proceed ...
}
The last thing I'm going to mention about the showModalDialog is that it works great even when the document displayed in the dialog is from a different domain. It's very common for us to have our javascript running from http://the-client.com but the "Terms of Service" web page is from http://the-enterprise-vendor.com
I need a temporary solution that I can deploy ASAP while we work on the long term solution. Here are my criteria:
minimal code change in existing JavaScript
the pop up window must be able to return a value to the "parent". Typically this value is a Boolean but it could be any simple type (e.g.: string, int, etc.)
solution must work even if the URL of the content is from different domain
Here's what I have so far:
1) Add the following method in my JavaScript:
function OpenDialog(url, width, height, callback)
{
var win = window.open(url, "MyDialog", width, height, "menubar=0,toolbar=0");
var timer = setInterval(function ()
{
if (win.closed)
{
clearInterval(timer);
var returnValue = win.returnValue;
callback(returnValue);
}
}, 500);
}
As you can see in this method, I try to make the pop up window look as similar to a dialog as possible by hiding the menu and the toolbar, I setup a time every 500 milliseconds to check if the window has been closed by the user and if so, get the 'returnValue' and invoke a callback.
2) replace all calls to showModalDialog with the following:
OpenDialog(myUrl, 875, 650, function (termsOfServiceAccepted)
{
if (termsOfServiceAccepted)
{
... proceed ....
}
});
The fourth parameter to the method is the callback where I check if the user has clicked the "Ok" button before allowing her to proceed.
I know it's a long question but basically it boils down to:
What do you think of the solution I propose?
In particular, do you think I'll be able to get a returnValue from a window that was opened with window.open?
Any other alternative you can suggest?

I have two ideas that could help you but the first one is tied to CORS, so you won't be able to use it from different domains at least you can access both services and configure them.
FIRST IDEA:
The first one is related to this native api. You could create on the parent window a global function like this:
window.callback = function (result) {
//Code
}
As you can see it receives a result argument which can hold the boolean value you need. The you could open the popup using the same old window.open(url) function. The popup's onlick event handler could look like this:
function() {
//Do whatever you want.
window.opener.callback(true); //or false
}
SECOND IDEA: Solves the problem
The other idea I got is to use this other native api to trigger an event on the parent window when the popup resolves (better known as cross-document messaging). So you could do this from the parent window:
window.onmessage = function (e) {
if (e.data) {
//Code for true
} else {
//Code for false
}
};
By this way you are listening to any posted message on this window, and checking if the data attached to the message is true (the user clicks ok in the popup) or false (the user clicks cancel in the popup).
In the popup you should post a message to the parent window attaching a true or a false value when corresponds:
window.opener.postMessage(true, '*'); //or false
I think that this solution perfectly fits your needs.
EDIT
I have wrote that the second solution was also tied to CORS but digging deeper
I realized that cross-document messaging isn't tied to CORS

Requiring confirmation from user before browser close _iff_ a Flex variable is true

I have a Flex application which allows the user to edit a cloud-based document. (Think SlideRocket.) When the user tries to navigate away or close the browser window, I'd like to show them an are-you-sure dialog iff they have unsaved changes.
I'm using the following custom class, which I found at Flash player notified on browser close or change page (as3). I don't think it is the problem.
package
{
import flash.external.ExternalInterface;
public class ExternalInterfaceUtil
{
public static function addExternalEventListener(qualifiedEventName:String, callback:Function, callBackAlias:String):void
{
// 1. Expose the callback function via the callBackAlias
ExternalInterface.addCallback( callBackAlias, callback );
// 2. Build javascript to execute
var jsExecuteCallBack:String = "document.getElementsByName('"+ExternalInterface.objectID+"')[0]."+callBackAlias+"()";
var jsBindEvent:String = "function(){"+qualifiedEventName+"= function(){"+jsExecuteCallBack+"};}";
// 3. Execute the composed javascript to perform the binding of the external event to the specified callBack function
ExternalInterface.call(jsBindEvent);
}
}
}
In my applicationComplete function, I add an event listener to the javascript window.onbeforeunload event, as follows:
ExternalInterfaceUtil.addExternalEventListener("window.onbeforeunload", requestUnloadConfirmation, "unloadConfirmation");
The Actionscript function requestUnloadConfirmation (below) is successfully called when the user tries to close the browser window. However, it does not prevent the browser from closing. (In Chrome, the browser closes and the Actionscript function is called subsequently. In Firefox, the browser stays open for the duration of the function but then closes.)
private function requestUnloadConfirmation():String {
if (changedSinceSave)
return "There are unsaved changes. Are you sure you want to leave without saving?";
else
return null;
}
Behavior is identical in both debug and release builds, and on the production server as well as the local machine.
Any help would be greatly appreciated,
Dave

Right now, when the JavaScript event is fired, it is set to call your function in your AS3 code, which it does. The JavaScript function, however, is not returning the value that your AS3 function returns. To get this behaviour, add 'return' to the JavaScript event-handling function created in addExternalEventListener like so:
var jsBindEvent:String = "function(){"+qualifiedEventName+"= function(){return "+jsExecuteCallBack+"};}";
Since the event handler should return a true or false value, your requestUnloadConfirmation function should have a return type of Boolean and return false to cancel the event, and true otherwise. Use the following to get a confirmation dialog box:
private function requestUnloadConfirmation():Boolean {
if (changedSinceSave)
return ExternalInterface.call("confirm", "There are unsaved changes. Are you sure you want to leave without saving?");
else
return false;
}
UPDATE:
It turns out that returning a string to window.onbeforeunload causes a confirmation dialog box to be shown automatically. The ExternalInterface.call to confirm causes a second dialog box to show; it is redundant. The only change required in the AS3 code is to add the "return" in the generated JavaScript.

In a regular html/javascript web-app you would use the window.onbeforeunload event to do this.
https://web.archive.org/web/20211028110528/http://www.4guysfromrolla.com/demos/OnBeforeUnloadDemo1.htm
Perhaps you can use this event, and check some value of your flex app to determine if you should ask the user (not familiar with flex...)?

I had to run some modifications in the above code to make it work.
The problem was due to the fact that the function which handles the event window.onbeforeunload, should not return any value to avoid popup confirmation and should return text value when a popup confirmation is in-order
Here are my changes:
private function requestUnloadConfirmation():String {
if (changedSinceSave){
return "There are unsaved changes. Are you sure you want to leave without saving?";
}
return null;
}
And a little change in embedded JS
var jsBindEvent:String = "function(){"+qualifiedEventName+"= function(){ if ("+jsExecuteCallBack+") return "+jsExecuteCallBack+"};}";

How can I override the OnBeforeUnload dialog and replace it with my own?

I need to warn users about unsaved changes before they leave a page (a pretty common problem).
window.onbeforeunload = handler
This works but it raises a default dialog with an irritating standard message that wraps my own text. I need to either completely replace the standard message, so my text is clear, or (even better) replace the entire dialog with a modal dialog using jQuery.
So far I have failed and I haven't found anyone else who seems to have an answer. Is it even possible?
Javascript in my page:
<script type="text/javascript">
window.onbeforeunload = closeIt;
</script>
The closeIt() function:
function closeIt()
{
if (changes == "true" || files == "true")
{
return "Here you can append a custom message to the default dialog.";
}
}
Using jQuery and jqModal I have tried this kind of thing (using a custom confirm dialog):
$(window).beforeunload(function () {
confirm('new message: ' + this.href + ' !', this.href);
return false;
});
which also doesn't work - I cannot seem to bind to the beforeunload event.

You can't modify the default dialogue for onbeforeunload, so your best bet may be to work with it.
window.onbeforeunload = function() {
return 'You have unsaved changes!';
}
Here's a reference to this from Microsoft:
When a string is assigned to the returnValue property of window.event, a dialog box appears that gives users the option to stay on the current page and retain the string that was assigned to it. The default statement that appears in the dialog box, "Are you sure you want to navigate away from this page? ... Press OK to continue, or Cancel to stay on the current page.", cannot be removed or altered.
The problem seems to be:
When onbeforeunload is called, it will take the return value of the handler as window.event.returnValue.
It will then parse the return value as a string (unless it is null).
Since false is parsed as a string, the dialogue box will fire, which will then pass an appropriate true/false.
The result is, there doesn't seem to be a way of assigning false to onbeforeunload to prevent it from the default dialogue.
Additional notes on jQuery:
Setting the event in jQuery may be problematic, as that allows other onbeforeunload events to occur as well. If you wish only for your unload event to occur I'd stick to plain ol' JavaScript for it.
jQuery doesn't have a shortcut for onbeforeunload so you'd have to use the generic bind syntax.
$(window).bind('beforeunload', function() {} );
Edit 09/04/2018: custom messages in onbeforeunload dialogs are deprecated since chrome-51 (cf: release note)

What worked for me, using jQuery and tested in IE8, Chrome and Firefox, is:
$(window).bind("beforeunload",function(event) {
if(hasChanged) return "You have unsaved changes";
});
It is important not to return anything if no prompt is required as there are differences between IE and other browser behaviours here.

While there isn't anything you can do about the box in some circumstances, you can intercept someone clicking on a link. For me, this was worth the effort for most scenarios and as a fallback, I've left the unload event.
I've used Boxy instead of the standard jQuery Dialog, it is available here: http://onehackoranother.com/projects/jquery/boxy/
$(':input').change(function() {
if(!is_dirty){
// When the user changes a field on this page, set our is_dirty flag.
is_dirty = true;
}
});
$('a').mousedown(function(e) {
if(is_dirty) {
// if the user navigates away from this page via an anchor link,
// popup a new boxy confirmation.
answer = Boxy.confirm("You have made some changes which you might want to save.");
}
});
window.onbeforeunload = function() {
if((is_dirty)&&(!answer)){
// call this if the box wasn't shown.
return 'You have made some changes which you might want to save.';
}
};
You could attach to another event, and filter more on what kind of anchor was clicked, but this works for me and what I want to do and serves as an example for others to use or improve. Thought I would share this for those wanting this solution.
I have cut out code, so this may not work as is.

1) Use onbeforeunload, not onunload.
2) The important thing is to avoid executing a return statement. I don't mean, by this, to avoid returning from your handler. You return all right, but you do it by ensuring that you reach the end of the function and DO NOT execute a return statement. Under these conditions the built-in standard dialog does not occur.
3) You can, if you use onbeforeunload, run an ajax call in your unbeforeunload handler to tidy up on the server, but it must be a synchronous one, and you have to wait for and handle the reply in your onbeforeunload handler (still respecting condition (2) above). I do this and it works fine. If you do a synchronous ajax call, everything is held up until the response comes back. If you do an asynchronous one, thinking that you don't care about the reply from the server, the page unload continues and your ajax call is aborted by this process - including a remote script if it's running.

This can't be done in chrome now to avoid spamming, refer to javascript onbeforeunload not showing custom message for more details.

Angular 9 approach:
constructor() {
window.addEventListener('beforeunload', (event: BeforeUnloadEvent) => {
if (this.generatedBarcodeIndex) {
event.preventDefault(); // for Firefox
event.returnValue = ''; // for Chrome
return '';
}
return false;
});
}
Browsers support and the removal of the custom message:
Chrome removed support for the custom message in ver 51 min
Opera removed support for the custom message in ver 38 min
Firefox removed support for the custom message in ver 44.0 min
Safari removed support for the custom message in ver 9.1 min

Try placing a return; instead of a message.. this is working most browsers for me.
(This only really prevents dialog's presents)
window.onbeforeunload = function(evt) {
//Your Extra Code
return;
}

You can detect which button (ok or cancel) pressed by user, because the onunload function called only when the user choise leaveing the page. Althoug in this funcion the possibilities is limited, because the DOM is being collapsed. You can run javascript, but the ajax POST doesn't do anything therefore you can't use this methode for automatic logout. But there is a solution for that. The window.open('logout.php') executed in the onunload funcion, so the user will logged out with a new window opening.
function onunload = (){
window.open('logout.php');
}
This code called when user leave the page or close the active window and user logged out by 'logout.php'.
The new window close immediately when logout php consist of code:
window.close();

I faced the same problem, I was ok to get its own dialog box with my message, but the problem I faced was :
1) It was giving message on all navigations I want it only for close click.
2) with my own confirmation message if user selects cancel it still shows the browser's default dialog box.
Following is the solutions code I found, which I wrote on my Master page.
function closeMe(evt) {
if (typeof evt == 'undefined') {
evt = window.event; }
if (evt && evt.clientX >= (window.event.screenX - 150) &&
evt.clientY >= -150 && evt.clientY <= 0) {
return "Do you want to log out of your current session?";
}
}
window.onbeforeunload = closeMe;

<script type="text/javascript">
window.onbeforeunload = function(evt) {
var message = 'Are you sure you want to leave?';
if (typeof evt == 'undefined') {
evt = window.event;
}
if (evt) {
evt.returnValue = message;
}
return message;
}
</script>
refer from http://www.codeprojectdownload.com

What about to use the specialized version of the "bind" command "one". Once the event handler executes the first time, it’s automatically removed as an event handler.
$(window).one("beforeunload", BeforeUnload);

Try this
$(window).bind('beforeunload', function (event) {
setTimeout(function () {
var retVal = confirm("Do you want to continue ?");
if (retVal == true) {
alert("User wants to continue!");
return true;
}
else {
window.stop();
return false;
}
});
return;
});