Open and Close Br window, but close it so it is gone.

I want to open a information popup and then have it close when focus is lost.
I find that the window closes, or I should say that focus is returned to the parent page, but  the
is still open in the background and you can be tabbed to it as a window.  I want it to be gone.



Here is my test case:
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<button onclick="myFunction()">Open</button>

<script>
function myFunction() {
    var myWindow = window.open('W4_tech_detail.php?Part_no=SGCU1CH','','scrollbars=yes,resizable=yes,width=700,height=600');
    myWindow.focus();
    myWindow.onblur=mywindow.close;    
}
</script>
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Here is my test URL :        https://www.eshowerdoor.com/test-window.html