Prompt User before browser close?

41,182

Solution 1

Update 2017

All modern browsers do not support custom messages any longer.

window.onbeforeunload = function(evt) {
   return true;
}

This one for closing the tab:

window.onbeforeunload = function(evt) {
    var message = 'Did you remember to download your form?';
    if (typeof evt == 'undefined') {
        evt = window.event;
    }
    if (evt) {
        evt.returnValue = message;
    }

    return message;
}

and use onClick event for logout button:

onClick="return confirm('Did you remember to download your form?');"

Solution 2

I think that this may be part of your problem:

else if(window.onbeforeunload) {
  window.onbeforeunload = unloadMess;
};

That test in the "if" statement will only be true if there's already a handler function. That test doesn't mean, "does the window object have an 'onbeforeunload' property?". It means, "is the 'onbeforeunload' property of the window currently not null?".

I think it'd be safe to just set "onbeforeunload" directly, for any browser.

Solution 3

You cannot alert or things like that in onbeforeunload, you cannot simply return false to make the user not leave the page, as with other events like onclick. This would allow a site to make it impossible to leave it.

You can however just return a string, the browser then shows a confirm dialog including your string asking the user whether they really want to leave.

41,182

JM4

I studied engineering/management of technology but got tossed into the world of web development after working years in a project management capacity. Work with healthcare/insurance companies to develop custom database and reporting solutions along with online enrollment applications.

Updated on December 05, 2020

Comments

JM4 over 3 years
We have an administrative portal that our teachers constantly forget to download their latest PDF instructions before logging out and/or closing the browser window. I have looked around but can't find what I'm looking for.

I want to accomplish the following goals:

Goal 1

Before a user can close the browser window, they are prompted "Did you remember to download your form?" with two options, yes/no. If yes, close, if no, return to page.

Goal 2

Before a user can click the 'logout' button, they are prompted with the same as above.

My first pass at the very basic code (which does not work for browser close) is:
```
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>

<script type="text/javascript">
function init() {
    if (window.addEventListener) {
        window.addEventListener("beforeunload", unloadMess, false);
    } else if (window.onbeforeunload) {
        window.onbeforeunload = unloadMess;
    };
}

function unloadMess() {
    var User_Message = "[Your user message here]"
    return User_Message;
}
</script>
</head>

<body onload="init();">
     hello this is my site
</body>
</html>
```
EDIT - NEW ISSUES

The solution provided below works but also has its own issues:

When user clicks the link to actually download the forms, the page thinks they are trying to leave and in turn present an error message to them! Also - I would like for one event or another to occur but not necessarily both. I.e. they hit 'logout' button and they are presented with the OnClick event, THEN the browser prompt. Any ideas?
Pointy almost 14 years

I thought I was right, but it turns out that both Firefox and IE will honor the "beforeunload" convention even when the browser window is being closed. The user does have a choice to let it close, however.
JM4 almost 14 years

I am not trying to prevent them from leaving, merely pointing out a script message and allowing them to select "yes or no"
JM4 almost 14 years

Yikes - only one issue, when they click the link to actually download the forms, the page thinks they are trying to leave and in turn present an error message to them!
Marian almost 14 years

@JM4: I know, but if it was possible an evil site could do it. As the Yes/No case is a rather commonly required one, it was made possible using the trick with the string.
Ryley almost 14 years

The evt object can tell you what was clicked (i.e. evt.target or window.event.srcElement depending on browser). So you could choose to do nothing in the case where they've clicked on the form.
Musaddiq Khan almost 7 years

It's not showing custom message on chrome. Default message Changes you made may not be saved. is displayed.