Center a popup window on screen?

Breaking down screen dynamics

Issues might arise when we want to center the popup across various screen sizes and resolutions. We need a Sherlock screenwidth - screenheight kind of deductions and also consider factors like zoom level, window frame, and whether we're centering with respect to the parent window or entire screen.

Presenting the popupCenter function

Say hello to possible future Diamond programming award, the popupCenter function. It takes into account the URL, title, width, and height to create and center the popup.

function popupCenter(url, title, w, h) {
  // Remember, two screens are better than one!
  const dualScreenLeft = window.screenLeft !== undefined ? window.screenLeft : window.screenX;
  const dualScreenTop = window.screenTop !== undefined ? window.screenTop : window.screenY;

  const width = window.innerWidth ? window.innerWidth : document.documentElement.clientWidth ? document.documentElement.clientWidth : screen.width;
  const height = window.innerHeight ? window.innerHeight : document.documentElement.clientHeight ? document.documentElement.clientHeight : screen.height;
  
  const systemZoom = width / window.screen.availWidth;
  const left = (width - w) / 2 / systemZoom + dualScreenLeft;
  const top = (height - h) / 2 / systemZoom + dualScreenTop;
  const newWindow = window.open(url, title, `scrollbars=yes, width=${w / systemZoom}, height=${h / systemZoom}, top=${top}, left=${left}`);

  // Focus, newWindow! You're in the spotlight now.
  if (window.focus) newWindow.focus();
}
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You are seeing it right, this function is the math geek that calculates effective center position of the popup, flexes its dynamic capabilities to fit multiple screens, session zoom levels, and outer window dimensions to perfectly stage the popup.

Pitfalls and Pro-Tips

While trying to center popups, beware the window.top monster as you might encounter domain restrictions issues with iframes. And yes, not all browsers are created equal. Some have different interface sizes and toolbars. So, the key is to test your popup in a variety of browser environments, adding another feather to your cross-browser compatibility hat.

Cross-resolution fits and finishes

For popups to sit right and tight across resolutions and aspect ratios, screen properties must be dynamically adjusted. The popupCenter function gets this to work with a finesse that Picasso would be proud of. It even handles adjustments for browser chrome to achieve the perfect fit.

Handling dual monitor scenarios

Remember, in a world where dual monitors are the norm, you need to make sure your popup window lands up in the right place, imitating a perfect parachute landing centred to the user’s current browser window, not just the primary screen. Our star popupCenter function lives up to this by acknowledging dualScreenLeft and dualScreenTop values.

User context: the guiding compass

User experience, is like your north star, guiding you to the right popup window creation and positioning. Your popup should be an aid to the user, either as an isolated task window or a contextual toolkit, the popupCenter impressively caters to both.