Forcefully stack an element on top by assigning it the highest z-Index possible.

stackOnTop.js

    /*
      Make sure the input element is the highest one in the page by z-index
      @param {DOM Element} el Element to stack at the top
      @param {DOM Element} ref BoundingClientRect reference of where to compare topl-left corner
    */    
    function stackOnTop(el, ref){

      // elementFromPoint returns null if element is outside visible viewport
      // scroll the page so the element comes into view
      if (window.innerHeight < ref.top){
        window.scrollTo(0, ref.top)
      }

      var hit = document.elementFromPoint(ref.left, ref.top - window.pageYOffset)

      while(!hit.isSameNode(el)){
        
        var zIndex = el.style.zIndex * 10
        console.info('again with z-index %d', zIndex)

        // see http://softwareas.com/whats-the-maximum-z-index
        if (zIndex > 2147483647){
          console.warn('screw this, I give up at z-index: ', zIndex)
          return
        }
        
        el.style.zIndex = zIndex
        stackOnTop(el, ref)
      }
    }