Untitled

var elem = $('div');
var count = elem.length;

var state = [];

var loop = function(){

  setTimeout(function(){
    elem.each(function(){
      var that = this;
      var $this = $(this);
      var height = Math.random() > 0.9? Math.random()*30 : (state.filter(function(a){ return a[0] == that; })[0] || [0, 0])[1]*0.9;
      state = state.filter(function(a){ return a[0] != that; }).concat([[that, height]]);
      $this.css({
        'background': '#fff',
        'bottom': height + 1,
        'height': height + 1
      });
    });
    loop();
  }, 30);

}

loop();