Window.OnFocus event does not work well with IE. Why?

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ASP.NET

Javascript

Hi All,

I have written a script that restrict users to stick to current window. If they lose focus for 3 times, your current page gets redirected to blank page.

Problem here is, it works fine with Mozilla and chrome, but while clicking anywhere within the window frame in IE, it gives me alert window which is not expected behavior.
Can anybody please explain me why?
Thank You.

Here is my script:

<script type="text/javascript">

$(function () {
            var count = 0;
            window.onfocus = function (event) {
            }
            window.onblur = function (event) {
                increase(count);
                if (count == 2) {
                    alert("Switching between views is not allowed");
                }
                else if (count == 3) {
                    alert("This window will be closed as you made maximum                                                                                     attempts");
                    var win = window.open(("about:blank", "_self");
                    //win.close();
                   }
            }
            function increase() {
                count++;
                return false;
            }
            
        });

</script>