How to Show the "Are You Sure You Want to Navigate Away from This Page" When Changes Committed

How to show the Are you sure you want to navigate away from this page? when changes committed?

Update (2017)

Modern browsers now consider displaying a custom message to be a security hazard and it has therefore been removed from all of them. Browsers now only display generic messages. Since we no longer have to worry about setting the message, it is as simple as:

// Enable navigation prompt
window.onbeforeunload = function() {
    return true;
};
// Remove navigation prompt
window.onbeforeunload = null;

Read below for legacy browser support.

Update (2013)

The orginal answer is suitable for IE6-8 and FX1-3.5 (which is what we were targeting back in 2009 when it was written), but is rather out of date now and won't work in most current browsers - I've left it below for reference.

The window.onbeforeunload is not treated consistently by all browsers. It should be a function reference and not a string (as the original answer stated) but that will work in older browsers because the check for most of them appears to be whether anything is assigned to onbeforeunload (including a function that returns null).

You set window.onbeforeunload to a function reference, but in older browsers you have to set the returnValue of the event instead of just returning a string:

var confirmOnPageExit = function (e) 
{
    // If we haven't been passed the event get the window.event
    e = e || window.event;

    var message = 'Any text will block the navigation and display a prompt';

    // For IE6-8 and Firefox prior to version 4
    if (e) 
    {
        e.returnValue = message;
    }

    // For Chrome, Safari, IE8+ and Opera 12+
    return message;
};

You can't have that confirmOnPageExit do the check and return null if you want the user to continue without the message. You still need to remove the event to reliably turn it on and off:

// Turn it on - assign the function that returns the string
window.onbeforeunload = confirmOnPageExit;

// Turn it off - remove the function entirely
window.onbeforeunload = null;

Original answer (worked in 2009)

To turn it on:

window.onbeforeunload = "Are you sure you want to leave?";

To turn it off:

window.onbeforeunload = null;

Bear in mind that this isn't a normal event - you can't bind to it in the standard way.

To check for values? That depends on your validation framework.

In jQuery this could be something like (very basic example):

$('input').change(function() {
    if( $(this).val() != "" )
        window.onbeforeunload = "Are you sure you want to leave?";
});

How to make the 'Are you sure you want to navigate away from this page' warning message in browser?

This is one of the multiple ways to achieve the same thing

function goodbye(e) {
    if(!e) e = window.event;
    //e.cancelBubble is supported by IE - this will kill the bubbling process.
    e.cancelBubble = true;
    e.returnValue = 'You sure you want to leave?'; //This is displayed on the dialog

    //e.stopPropagation works in Firefox.
    if (e.stopPropagation) {
        e.stopPropagation();
        e.preventDefault();
    }
}
window.onbeforeunload=goodbye;

got it from here open js

How to avoid the “Are you sure you want to navigate away from this page?” when changes committed? on pagination click of gridview in IE

just set the the value to null on pagination click

   window.onbeforeunload = null;

UPDATE 1

try this one instead of your code:

  var myEvent = window.attachEvent || window.addEventListener;
    var chkevent = window.attachEvent ? 'onbeforeunload' : 'beforeunload'; /// make IE7, IE8 compitable
    myEvent(chkevent, function (e) { // For >=IE7, Chrome, Firefox
        var confirmationMessage = 'Are you sure to leave the page?';  // a space
        (e || window.event).returnValue = confirmationMessage;
        return confirmationMessage;
    });

UPDATE 2

after you use window.onbeforeunload = null; in your pagination control to rebind the alert in your update panel try this solution, it may help you with that issue:

   $(document).ready(function () {
     bindPageAlert();
   });

    function bindPageAlert()
    {
        var myEvent = window.attachEvent || window.addEventListener;
        var chkevent = window.attachEvent ? 'onbeforeunload' : 'beforeunload';
        myEvent(chkevent, function (e) { // For >=IE7, Chrome, Firefox
            var confirmationMessage = 'Are you sure to leave the page?';  // a space
            (e || window.event).returnValue = confirmationMessage;
            return confirmationMessage;
        });
    }

    Sys.WebForms.PageRequestManager.getInstance().add_endRequest(bindPageAlert);

How to prevent Are you sure you want to navigate away from this page? alert on form submission?

stackoverflow reference

To turn it on:

window.onbeforeunload = "Are you sure you want to leave?";

To turn it off:

window.onbeforeunload = null;

Bear in mind that this isn't a normal event - you can't bind to it in the standard way.

To check for values? That depends on your validation framework.

In jQuery this could be something like (very basic example):

$('input').change(function() {
    if( $(this).val() != "" )
        window.onbeforeunload = "Are you sure you want to leave?";
});

With JQuery this stuff is pretty easy to do. Since you can bind to sets.

Its NOT enough to do the onbeforeunload, you want to only trigger the navigate away if someone started editing stuff.

To make this work in Chrome and Safari, you would have to do it like this

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

    var msg = "Sure you want to leave?";

    // For IE and Firefox prior to version 4
    if (e) {
        e.returnValue = msg;
    }

    // For Safari
    return msg;
};

This is the general rule in reference

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

  // For IE<8 and Firefox prior to version 4
  if (e) {
    e.returnValue = 'Any string';
  }

  // For Chrome, Safari, IE8+ and Opera 12+
  return 'Any string';
};

reference: https://developer.mozilla.org/en/DOM/window.onbeforeunload

Alerts when navigating away from a web page

By the browser. It's the beforeunload event handler that returns the customized text of the dialog, which is only the middle of the three paragraphs - the other two paragraphs as well as the text of the buttons cannot be customized or otherwise changed.

window.onbeforeunload = function(){ return 'Testing...' }

// OR

var unloadListener = function(){ return 'Testing...' };
window.addEventListener('beforeunload', unloadListener);

Will yield a dialog that says

Are you sure you want to navigate away from this page?

Testing...

Press OK to continue, or Cancel to stay on the current page.

You can nullify this by setting the handler to null

window.onbeforeunload = null;

// OR

window.removeEventListener('beforeunload', unloadListener);

Adding a are you sure you want to leave this page alert message when exiting a shiny app

The easiest way to achieve this is to use window.onbeforeunload in JavaScript.

Code from the accepted answer in another Stackoverflow topic:

window.onbeforeunload = function() {
  return 'Your changes will be lost!';
};

You can implement this (and any JavaScript code), by including it in fluidPage for Shiny apps, or dashboardBody for Shiny dashboard pages.

The JavaScript code needs to be wrapped in head and script tags (same as when you include a JS file in HTML)

Solution:

tags$head(tags$script(HTML("
    // Enable navigation prompt
    window.onbeforeunload = function() {
        return 'Your changes will be lost!';
    };
"))),

Reproducible example for the default Geyser app:

library(shiny)

# Define UI for application that draws a histogram
ui <- fluidPage(
    # Navigation prompt
    tags$head(tags$script(HTML("
        // Enable navigation prompt
        window.onbeforeunload = function() {
            return 'Your changes will be lost!';
        };
    "))),
    # Application title
    titlePanel("Old Faithful Geyser Data"),

    # Sidebar with a slider input for number of bins 
    sidebarLayout(
        sidebarPanel(
            sliderInput("bins",
                        "Number of bins:",
                        min = 1,
                        max = 50,
                        value = 30)
        ),

        # Show a plot of the generated distribution
        mainPanel(
           plotOutput("distPlot")
        )
    )
)

# Define server logic required to draw a histogram
server <- function(input, output) {

    output$distPlot <- renderPlot({
        # generate bins based on input$bins from ui.R
        x    <- faithful[, 2]
        bins <- seq(min(x), max(x), length.out = input$bins + 1)

        # draw the histogram with the specified number of bins
        hist(x, breaks = bins, col = 'darkgray', border = 'white')
    })
}

# Run the application 
shinyApp(ui = ui, server = server)

Warn user before leaving web page with unsaved changes

Short, wrong answer:

You can do this by handling the beforeunload event and returning a non-null string:

window.addEventListener("beforeunload", function (e) {
    var confirmationMessage = 'It looks like you have been editing something. '
                            + 'If you leave before saving, your changes will be lost.';

    (e || window.event).returnValue = confirmationMessage; //Gecko + IE
    return confirmationMessage; //Gecko + Webkit, Safari, Chrome etc.
});

The problem with this approach is that submitting a form is also firing the unload event. This is fixed easily by adding the a flag that you're submitting a form:

var formSubmitting = false;
var setFormSubmitting = function() { formSubmitting = true; };

window.onload = function() {
    window.addEventListener("beforeunload", function (e) {
        if (formSubmitting) {
            return undefined;
        }

        var confirmationMessage = 'It looks like you have been editing something. '
                                + 'If you leave before saving, your changes will be lost.';
        
        (e || window.event).returnValue = confirmationMessage; //Gecko + IE
        return confirmationMessage; //Gecko + Webkit, Safari, Chrome etc.
    });
};

Then calling the setter when submitting:

<form method="post" onsubmit="setFormSubmitting()">     
    <input type="submit" />
</form>

But read on...

Long, correct answer:

You also don't want to show this message when the user hasn't changed anything on your forms. One solution is to use the beforeunload event in combination with a "dirty" flag, which only triggers the prompt if it's really relevant.

var isDirty = function() { return false; }

window.onload = function() {
    window.addEventListener("beforeunload", function (e) {
        if (formSubmitting || !isDirty()) {
            return undefined;
        }
        
        var confirmationMessage = 'It looks like you have been editing something. '
                                + 'If you leave before saving, your changes will be lost.';

        (e || window.event).returnValue = confirmationMessage; //Gecko + IE
        return confirmationMessage; //Gecko + Webkit, Safari, Chrome etc.
    });
};

Now to implement the isDirty method, there are various approaches.

You can use jQuery and form serialization, but this approach has some flaws. First you have to alter the code to work on any form ($("form").each() will do), but the greatest problem is that jQuery's serialize() will only work on named, non-disabled elements, so changing any disabled or unnamed element will not trigger the dirty flag. There are workarounds for that, like making controls readonly instead of enabling, serializing and then disabling the controls again.

So events seem the way to go. You can try listening for keypresses. This event has a few issues:

Won't trigger on checkboxes, radio buttons, or other elements that are being altered through mouse input.
Will trigger for irrelevant keypresses like the Ctrl key.
Won't trigger on values set through JavaScript code.
Won't trigger on cutting or pasting text through context menus.
Won't work for virtual inputs like datepickers or checkbox/radiobutton beautifiers which save their value in a hidden input through JavaScript.

The change event also doesn't trigger on values set from JavaScript code, so also won't work for virtual inputs.

Binding the input event to all inputs (and textareas and selects) on your page won't work on older browsers and, like all event handling solutions mentioned above, doesn't support undo. When a user changes a textbox and then undoes that, or checks and unchecks a checkbox, the form is still considered dirty.

And when you want to implement more behavior, like ignoring certain elements, you'll have even more work to do.

Don't reinvent the wheel:

So before you think about implementing those solutions and all required workarounds, realize you're reinventing the wheel and you're prone to running into problems others have already solved for you.

If your application already uses jQuery, you may as well use tested, maintained code instead of rolling your own, and use a third-party library for all of this.

jquery.dirty (suggested by @troseman in the comments) provides functions for properly detecting whether a form has been changed or not, and preventing the user from leaving the page while displaying a prompt. It also has other useful functions like resetting the form, and setting the current state of the form as the "clean" state. Example usage:

$("#myForm").dirty({preventLeaving: true});

An older, currently abandoned project, is jQuery's Are You Sure? plugin, which also works great; see their demo page. Example usage:

<script src="jquery.are-you-sure.js"></script>

<script>
  $(function() {
    $('#myForm').areYouSure(
      {
        message: 'It looks like you have been editing something. '
               + 'If you leave before saving, your changes will be lost.'
      }
    );
  });
  
</script>

Custom messages not supported everywhere

Do note that since 2011 already, Firefox 4 didn't support custom messages in this dialog. As of april 2016, Chrome 51 is being rolled out in which custom messages are also being removed.

Some alternatives exist elsewhere on this site, but I think a dialog like this is clear enough:

Do you want to leave this site?
Changes you made may not be saved.
Leave Stay

How to Show the "Are You Sure You Want to Navigate Away from This Page" When Changes Committed