Take a look at this StackOverflow's post Center a popup window on screen?
I've made a little upgrade for that function a couple of years ago.
function multipleScreenPopup(url, title, w, h, centered = true, moveRight = 0, moveDown = 0, resizable = "no") {
// Fixes dual-screen position Most browsers Firefox
var dualScreenLeft = window.screenLeft != undefined ? window.screenLeft : screen.left;
var dualScreenTop = window.screenTop != undefined ? window.screenTop : screen.top;
var width = window.innerWidth ? window.innerWidth : document.documentElement.clientWidth ? document.documentElement.clientWidth : screen.width;
var height = window.innerHeight ? window.innerHeight : document.documentElement.clientHeight ? document.documentElement.clientHeight : screen.height;
var left = 0;
var top = 0;
if (centered === true) {
left = ((width / 2) - (w / 2)) + dualScreenLeft;
top = ((height / 2) - (h / 2)) + dualScreenTop;
} else {
left = dualScreenLeft + moveRight;
top = dualScreenTop + moveDown;
}
var newWindow = window.open(url, title, 'directories=no,titlebar=no,toolbar=no,location=no,status=no,menubar=no,scrollbars=yes,resizable=' + resizable + ', width=' + w + ', height=' + h + ', top=' + top + ', left=' + left);
// Puts focus on the newWindow
if (window.focus) {
newWindow.focus();
}
}
// centered as of the monitor that fired on it
multipleScreenPopup('https://google.com', '_blank', 500, 500);
// move from the left and from the top
multipleScreenPopup('https://yahoo.com', '_blank', 500, 500, false, 200, 200);