jQuery function to detect if element is within viewport

isonscreen.js

// If element is in viewport
  // EXAMPLE: $('.element').isOnScreen();
  $.fn.isOnScreen = function(){

    var win = $(window);

    var viewport = {
      top : win.scrollTop(),
      left : win.scrollLeft()
    };
    viewport.right = viewport.left + win.width();
    viewport.bottom = viewport.top + win.height();

    var bounds = this.offset();
    bounds.right = bounds.left + this.outerWidth();
    bounds.bottom = bounds.top + this.outerHeight();

    return (!(viewport.right < bounds.left || viewport.left > bounds.right || viewport.bottom < bounds.top || viewport.top > bounds.bottom));

  };