Bootstrap tooltip auto placement to prevent tooltip dropping off screen

autoPlacement.js

var autoPlacement = function (tip, element) {
  var $document = $(document);
  var offset = $(element).offset();
  var height = $document.outerHeight();
  var width = $document.outerWidth();
  var vert = 0.5 * height - offset.top;
  var horiz = 0.5 * width - offset.left;
  if (Math.abs(horiz) > Math.abs(vert)) {
      return horiz > 0 ? 'right' : 'left';
  }
  return vert > 0 ? 'bottom' : 'top';
};

$('el').tooltip({
placement: autoPlacement,
trigger: 'hover',
html: true
});