Alert When Browser Window Closed Accidentally

Alert when browser window closed accidentally

We should prevent or prompt user that on performing these actions he will lose his data.

Click on back browser button.
Click on refresh browser button.
Click on close button of browser.
Click of forward browser button.
Keyboard stroke- Alt+F4 (Close)
Keyboard stroke- F5 (Refresh)
Keyboard stroke-CTRL+ F5 (Refresh)
Keyboard stroke-Shift+ F5 (Refresh)
Change of url
Or anything that cause postback other than your particular submit button.

To explain that I have used two textboxes, one Asp.net submit button with id TestButton.
Other postback controls that I have taken are
One other asp.net button,one checkbox with autopostback property true,one dropdownlist with autopostback property true.
Now I have used all these postback controls so that to show you that we also need to show promt to user about the data lose when user perform actions on these controls.
On submit button we will not show the prompt as we have to submit the data with that control action.Here is the sample code.I have set window.onbeforeunload method on controls change.

<html >
<head id="Head1">
    <title></title>

    <script type="text/javascript"
            src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></script>

    <script type="text/javascript">
        $(function()
        {
            // Prevent accidental navigation away
            $(':input').bind(
                'change', function() { setConfirmUnload(true); });
            $('.noprompt-required').click(
                function() { setConfirmUnload(false); });

            function setConfirmUnload(on)
            {
                window.onbeforeunload = on ? unloadMessage : null;
            }
            function unloadMessage()
            {
                return ('You have entered new data on this page. ' +
                        'If you navigate away from this page without ' +
                        'first saving your data, the changes will be lost.');
            }

            window.onerror = UnspecifiedErrorHandler;
            function UnspecifiedErrorHandler()
            {
                return true;
            }

        }); 

    </script>

</head>
<body>
    <form id="form1" name="myForm" runat="server">
    <div>
        First Name :<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox><br />
        <br />
        Last Name :<asp:TextBox ID="TextBox2" runat="server"></asp:TextBox><br />
        <br />
        IsMarried :<asp:CheckBox ID="CheckBox1" runat="server" /><br />
        <br />
        <asp:Button runat="server" ID="TestButton" Text="Submit" CssClass="noprompt-required" /><br />
        <br />
        <br />
        <br />
        <br />
        <asp:Button runat="server" ID="AnotherPostbackButton" Text="AnotherPostbackButton"
             /><br />
        <br />
        <asp:CheckBox runat="server" ID="CheckboxWhichCausePostback" Text="CheckboxWhichCausePostback"
            AutoPostBack="true" /><br />
        <br />
        DropdownWhichCausePostback<asp:DropDownList runat="server" ID="DropdownWhichCausePostback"
            AutoPostBack="true">
            <asp:ListItem Text="Text1"></asp:ListItem>
            <asp:ListItem Text="Text2"></asp:ListItem>
        </asp:DropDownList>
        <br />
        <br />
    </div>
    </form>
</body>

Above I have used:

$('.noprompt-required').click(function() { setConfirmUnload(false); });

What I have done in this line is I am calling setConfirmUnload method and passing false as argument which will set the window.onbeforeunload to null.
So what that means is on any control where you want that user should not be prompted, give that control the class .noprompt-required and leave other as it is.

Displays message when are Tab closed By State Status in React

After searching I found the code that does it

const [state, setState] = React.useState(false);
  useEffect(() => {
    const cb = e => {
      if (state) {
        console.log({ s: state });
        e.preventDefault();
        e.returnValue = "Are you sure?";
      }
    };
    window.addEventListener("beforeunload", cb);
    return () => window.removeEventListener("beforeunload", cb);
  }, [state]);

I am attaching an example

codesandbox

Reactjs Browser Tab Close Event

What you did is correct apart from the event name and the fact that alert will be blocked in that particular event.

You can show a message like this:

window.addEventListener("beforeunload", (ev) => 
{  
    ev.preventDefault();
    return ev.returnValue = 'Are you sure you want to close?';
});

Hope this helps.

Alert When Browser Window Closed Accidentally