lazy load not work in bootstrap carousel

Question

I create carousel using bootstrap 3 like this :

HTML :

<div id="myCarousel" class="carousel slide">
    <div class="carousel-inner">
        <div class="active item">
            <img src="http://rivathemes.net/html/envor/img/posts/3.jpg" class="img-big">
        </div>
        <div class="item">
            <img data-lazy-load-src="http://rivathemes.net/html/envor/img/posts/4.jpg" class="img-big">
        </div>
    </div>
    <div class="carousel-controls">
<a class="left carousel-control" href="#myCarousel" data-slide="prev"><i class="fa fa-angle-double-left fa-lg"></i></a>

<a class="right carousel-control" href="#myCarousel" data-slide="next"><i class="fa fa-angle-double-right fa-lg"></i></a>

    </div>
</div>

and add this code for add img lazy load.

JS :

$('#myCarousel').on('slid', function () {
    var $nextImage = $('.active.item', this).next('.item').find('img');
    $nextImage.attr('src', $nextImage.data('lazy-load-src'));
});

But, This not work for me!? can do fix this ?

Important Q: can i add image preloader for lazy load?!

DEMO : FIDDLE

Answer 1

The answer by dm4web does not account for skipping slides by directly clicking the carousel indicators. This version correctly loads an image regardless of how you slide to it, using Bootstrap's event.relatedTarget (the item being slid into place, see the official documentation). Try running the snippet below and clicking on the indicators to switch several slides ahead.

var cHeight = 0;

$('#carousel-example-generic').on('slide.bs.carousel', function(e) {

  var $nextImage = $(e.relatedTarget).find('img');

  $activeItem = $('.active.item', this);

  // prevents the slide decrease in height
  if (cHeight == 0) {
    cHeight = $(this).height();
    $activeItem.next('.item').height(cHeight);
  }

  // prevents the loaded image if it is already loaded
  var src = $nextImage.data('lazy-load-src');

  if (typeof src !== "undefined" && src != "") {
    $nextImage.attr('src', src)
    $nextImage.data('lazy-load-src', '');
  }
});

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css" rel="stylesheet" />
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>

<div class="container-fluid">

  <div id="carousel-example-generic" class="carousel slide" data-ride="carousel">
    <!-- Indicators -->
    <ol class="carousel-indicators">
      <li data-target="#carousel-example-generic" data-slide-to="0" class="active"></li>
      <li data-target="#carousel-example-generic" data-slide-to="1"></li>
      <li data-target="#carousel-example-generic" data-slide-to="2"></li>
      <li data-target="#carousel-example-generic" data-slide-to="3"></li>
      <li data-target="#carousel-example-generic" data-slide-to="4"></li>
    </ol>

    <!-- Wrapper for slides -->
    <div class="carousel-inner" role="listbox">
      <div class="item active">
        <img src="http://placehold.it/5000x1000">
      </div>
      <div class="item">
        <img data-lazy-load-src="http://placehold.it/5001x1000">
      </div>
      <div class="item">
        <img data-lazy-load-src="http://placehold.it/5002x1000">
      </div>
      <div class="item">
        <img data-lazy-load-src="http://placehold.it/5003x1000">
      </div>
      <div class="item">
        <img data-lazy-load-src="http://placehold.it/5004x1000">
      </div>
    </div>

    <!-- Controls -->
    <a class="left carousel-control" href="#carousel-example-generic" role="button" data-slide="prev">
      <span class="glyphicon glyphicon-chevron-left" aria-hidden="true"></span>
      <span class="sr-only">Previous</span>
    </a>
    <a class="right carousel-control" href="#carousel-example-generic" role="button" data-slide="next">
      <span class="glyphicon glyphicon-chevron-right" aria-hidden="true"></span>
      <span class="sr-only">Next</span>
    </a>
  </div>

</div>

Answer 2

http://jsfiddle.net/ys4je40u/

1. add lazy-load class to item object
2. use slide.bs.carousel event

CSS:

.lazy-load {
    background: url("http://www.mozart.it/images/preloader.gif") center center no-repeat;
}

JQ:

var cHeight = 0;

$('#myCarousel').on('slide.bs.carousel', function (e) {
    var $nextImage = null;

    $activeItem = $('.active.item', this);

    if (e.direction == 'left'){
        $nextImage = $activeItem.next('.item').find('img');
    } else {
        if ($activeItem.index() == 0){
            $nextImage = $('img:last', $activeItem.parent());
        } else {
            $nextImage = $activeItem.prev('.item').find('img');
        }
    }

    // prevents the slide decrease in height
    if (cHeight == 0) {
       cHeight = $(this).height();
       $activeItem.next('.item').height(cHeight);
    }

    // prevents the loaded image if it is already loaded
    var src = $nextImage.data('lazy-load-src');

    if (typeof src !== "undefined" && src != "") {
       $nextImage.attr('src', src)
       $nextImage.data('lazy-load-src', '');
    }
});