11 January 2009

Update: Creating a news carousel with jQuery, now with time based switching

This is just a simple and quick update on the Creating a news carousel with jQuery post.

After reading this comment, and going through the code, I decided to implement the time-based switching functionality and also clean up the code a little bit (check it out here).

The additions made (along with some code cleaning) were:

  • Append a simple div that will shrink while the picture is shown and reinitialized when the picture is switched.
  • Add a setInterval call that will do the picture switching (and the new div's animation).

Update 01/12: I added some fixes to the code

  • Use the image's load event to calculate each individual width. When all images are loaded, then the carousel is initiated.
  • The animate_timer function now stops all animations on the timer div before reinitializing the animation
Update 01/27: Even more fixes :)
  • Work with cases were images are already in cache and load event is fired before we attach to it.
  • Fixed the way the news animation was calculated.
  • Added 2 more news to help test it better.

So here's the new javascript that will do this:

$(function() {
    var carousel   = $('#news_carousel');
    var news       = carousel.find('ul.news');
    var controls   = null; // Will hold the ul with the controls
    var timer      = null; // Will hold the timer div
    var wait       = 5000; // Milliseconds to wait for auto-switching
    var widths     = [];   // Will hold the widths of each image
    var items_size = news.find('li').length;
    var initialized = false;

    if (!items_size) { return; }

    // Controls html to append
    var controls_str = '<ul class="controls">';
    for ( var i = 1; i <= items_size; i++) {
       controls_str += '<li><a href="#">' + i + '</a></li>';
    controls_str += '</ul>';

    // Cache the controls list
    controls = carousel.append(controls_str).find('ul.controls');

    // Make the first button in controls active
    controls.find('li:first a').addClass('active');

    // Hook to the controls' click events
    controls.find('li a').click(function(event) {
      move_news( $(this) );
      return false;

    // Append the timer and cache it
    timer = carousel.append('<div class="timer"></div>').find('div.timer');

    // Store each item's width and calculate the total width
    news.find('li img')
        .each(function(i, e) {
            widths[i] = $(e).width();
            if ( all_images_loaded() ) { init_carousel(); }
        .load(function(e) {
            var i = news.find('li img').index(this);
            widths[i] = $(this).width();
            if ( all_images_loaded() ) { init_carousel(); }

    function all_images_loaded() {
      if (items_size == widths.length) && (jQuery.inArray(0, widths)  1 ) {
        return false;

      var current_active = controls.find('li a.active');

      if (new_active == 'next') {
        var next = current_active.parent().next().find('a');

        if ( !next.length ) { next = controls.find('li:first a'); }

        new_active = next;

      var current_index = parseInt(current_active.text(), 10) - 1;
      var new_index     = parseInt(new_active.text(), 10) - 1;
      var move_to       = new_index - current_index;

      if (!move_to) { return false; }

      var direction = (move_to > 0)? '-=': '+=';

      var move   = 0;
      var bottom = Math.min(current_index, new_index);
      var top    = Math.max(current_index, new_index);

      while (bottom < top) {
        move += widths[bottom];

      news.animate({marginLeft: direction + move }, 500);

    function animate_timer() {
      timer.stop().css({width: '100px'}).animate({width: '1px'}, wait);

    // Initializer, called when all images are loaded
    function init_carousel() {
      if (initialized) { return false; }

      // Set the news ul total width
      var width = 0;
      for( var i = 0; i < widths.length; i++) { width += widths[i]; }

      // Make the news change every X seconds
      setInterval(function() { move_news('next'); animate_timer(); }, wait);

      initialized = true;

05 October 2008

Creating a news carousel with jQuery

Last week I had to do a news carousel for a project I'm developing. It had been a while since I had the chance to do something interesting with jQuery, so I wanted to share the experience of how easily you can build similar widgets for your site.

So first let's take a look at what we want to build.

Now, I know that there are a few plugins out there for jQuery that probably can do this, but the point of this post is to show how simple it is to create something like this with a few lines of jQuery and CSS.

Let's begin by defining how we will organize the content. Being a list of news, we can either use an ordered or an unordered list.

<div id="news_carousel">
  <ul class="news">
      <img src="" alt="" />
      <strong><a href="#">Title</a></strong>

Now that we have our content, we have to style it. The keys here are to:

  • Align the list elements one next to the other.
  • Make #news_carousel just show one list element at a time
  • Use relative and absolute positioning to show the titles and descriptions over each image

Here's the CSS used in the sample with some comments:

 #news_carousel {
     width: 444px;
     height: 333px;
     margin: 0;
     padding: 0;
     overflow: hidden;  /* this will make only show 1 li */
     position: relative;
  #news_carousel ul.news {
    list-style-type: none;
    margin: 0;
    padding: 0;
    position: relative;
  #news_carousel ul li {
    margin: 0;
    padding: 0;
    position: relative;
    /* to do absolute positioning of the child paragraph */
    float: left;
    /* align one next to the other */
  #news_carousel ul.news li p {
    position: absolute;
    bottom: 10px;
    left: 0;
    margin: 5px;
  #news_carousel ul.news li p strong {
    display: block;
    padding: 5px;
    margin: 0;
    font-size: 20px;
    background: #444;
  #news_carousel ul.news li p span {
    padding: 2px 5px;
    color: #000;
    background: #fff;
  #news_carousel ul.controls {
    position: absolute;
    top: 0px; right: 20px;
    list-style-type: none;
  #news_carousel ul.controls li a {
    float: left;
    font-size: 15px;
    margin: 5px;
    padding: 2px 7px;
    background: #000;
    text-decoration: none;
    outline: none;
  #news_carousel ul.controls li a.active {
    border: 2px solid #ccc;

The Javascript code is pretty self-explanatory:

var news_carousel = function() {
    var items_size = $('#news_carousel ul li').length;

    if (items_size == 0) return;

    // Calculate the total width and set that value to
    //   the ul.news width
    // Store each item width
    var width = 0;
    var widths = [];
    $('#news_carousel ul.news li img').each(function(i, e) {
      widths[i] = $(e).width();
      width += widths[i];

    $("#news_carousel ul.news").width(width);

    // Append the controls
    controls = '<ul class="controls"><li><a class="active" href="#">1</a>';
    for ( var i = 2; i <= items_size; i++) {
       controls += '</li><li><a href="#">' + i + '</a></li>';
    controls += '</ul>';

    $('#news_carousel ul.controls li a').click(function(event) {
      // if the ul is already moving, then do nothing
      if ($("#news_carousel ul.news:animated").length > 0) return false;

      var clicked_item = $(event.target);
      var current_active = $("#news_carousel ul.controls li a.active");
      var current_index = parseInt(current_active.text());
      var new_index = parseInt(clicked_item.text());
      var move = new_index - current_index; //how many items it should be moved

      if (move != 0) {
        direction = (move > 0)? "-=": "+=";
        $('#news_carousel ul.news')
          .animate({marginLeft: direction + widths[new_index-1] }, 300);

      return false;

And that's it! Around 100 lines of code and you have your own home-made news carousel. Hope you found it useful! :)

(Pictures taken from: http://www.flickr.com/photos/christing/268490607/ and http://www.flickr.com/photos/11717181@N02/1170861540/.)