How to center align pop up div using Javascript

Question

How to align a pop up division to center of monitor/screen using javascript?

I tried using screen.width and screen.height to get center. But the division gets aligned to center of scrolling page vertically

Thanks in advance for any help and suggestions

Answer 1

Try this:

<div id="popup" class="popup">
  This a vertically and horizontally centered popup.
</div>

<a onclick="showPopup('popup');">Show Popup</a>

<style type="text/css">
  .popup {
    width:200px;
    height:100px;
    position:absolute;
    top:50%;
    left:50%;
    margin:-50px 0 0 -100px; /* [-(height/2)px 0 0 -(width/2)px] */
    display:none;
  }
</style>

<script type="text/javascript">
  function showPopup(id) {
    var popup = document.getElementById(id);
    popup.style.display = 'block';
  }
</script>

CSS explained: The div is 200x100, you position it 50% from the top and 50% from the left, but to have it centered fully, you need to substract from that 50% values the half of the width and height, the way to do this is to use negative margins, hence margin-top should be the negative value of the height/2 and margin-left should be the negative value of the width/2.