@media screen and (-ms-high-contrast: active), (-ms-high-contrast: none) { 
    /* IE10-11 */ 
}

var margin = 15;  // 15px отступ для наглядности

$('.container').on('resize scroll', function() {

  var $container = $(this);
  var container_height = $container.outerHeight();

  $('.block').each(function(i, block) {
    var $block = $(block);
    
    var top = $block.offset().top - $container.offset().top;
    var bottom = top + $block.outerHeight();

    var is_visible = (bottom > (0 + margin) && top < (container_height - margin));

    $block[is_visible ? 'addClass' : 'removeClass']('block-visible');
  });
}).trigger('scroll');

$str = '"1"=>"1", "2"=>"3"';
serialize(array($str));

$str = array("1"=>"1", "2"=>"3");
serialize($str);