Load more with Ajax

Intro
The standard template
The controller
The JSON template
The JavaScript
Include JavaScript in footer
If Javascript is not available…
Download files

Intro

Note: This tutorial makes use of the content representations feature introduced in Kirby 2.4. With a few changes, you can also make this work in older versions of Kirby.

This tutorial assumes that you have a page called projects in /content with some project subpages. For the example to work, the text file in /projects must be called projects.txt.

Do not put the HTML comment tags  in the code examples below into your files, they are just there to indicate file names.

Often, you only want to show a limited number of projects, articles or images on a page when it is first loaded. If users want to see more, they can click or tap a button and additional content is appended to the DOM. In this tutorial, we'll go through the steps that are needed to achieve this with Kirby.

Here's a quick wrap-up of what we'll be doing:

We start with a projects page where we display a limited number of projects with their image and title. When the user clicks a "load more" button, our JavaScript event listener makes an Ajax call to the JSON representation of our template. If the call is successful, the content is appended to the page.

The standard template

Let's start with the projects.php template.

<!-- /site/templates/projects.php -->
<?php snippet('header') ?>

  <main class="main" role="main">
    <h1><?= $page->title()->html() ?></h1>
    <?= $page->text()->kirbytext() ?>

    <ul class="projects" data-page="<?= $page->url() ?>" data-limit="<?= $limit ?>">

      <!-- Loop through the projects -->
      <?php foreach($projects as $project): ?>
        <?php snippet('project', compact('project')) ?>
      <?php endforeach ?>

    </ul>
    <button class="load-more">Load more</button>

  </main>

<?php snippet('footer') ?>

We put the list item for each project in a separate snippet. We'll need that a second time and can avoid to write redundant code that way.

<!-- /site/snippets/project.php -->
<li class="project">
  <a href="<?= $project->url() ?>" class="project-link">
    <!-- We want to get the first image of each project. We first check if it exists! -->
    <?php if($image = $project->image()): ?>
    <img src="<?= $image->url() ?>" alt="<?= $image->alt_text()->html() ?>" />
    <?php endif ?>
    <div class="project-caption">
      <h2 class="project-title"><?= $project->title()->html() ?></h2>
    </div>
  </a>
</li>

Apart from our HTML for the project, we have included a button with the class load-more. Also, we added two data attributes data-page and data-limit to pass the current page and the limit value to our JavaScript code.

You will probably have noticed that we haven't defined the variable $projects yet, so PHP would issue a warning if we tried to load the page. We'll catch up on this now in our projects.php controller.

The controller

The controller is the place where we add our template logic:

<!-- /site/controllers/projects.php -->
<?php

return function($site, $pages, $page) {

  $projects = $page->children()->visible();
  $count    = $projects->count();
  $more     = false;

  // check if the request is an Ajax request and if the limit and offset keys are set
  if(r::ajax() && get('offset') && get('limit')) {

    // convert limit and offset values to integer
    $offset = intval(get('offset'));
    $limit  = intval(get('limit'));

    // limit projects using offset and limit values
    $projects = $projects->offset($offset)->limit($limit);

    // check if there are more projects left
    $more = $count > $offset + $limit;

  // otherwise set the number of projects initially displayed
  } else {

    $offset   = 0;
    $limit    = 2;
    $projects = $projects->limit($limit);

  }

  return compact('offset', 'limit', 'projects', 'more');

};

First, we fetch all visible children of the projects page and store it in the $projects variable. We also store the number of subpages in $count.

Then we check if the request is an Ajax request, and if the request contains the offset and limit keys:

if(r::ajax() && get('offset') && get('limit')) {

// ...

} else {

  $offset   = 0;
  $limit    = 2;
  $projects = $projects->limit($limit);
}

If the request is not an Ajax request, we set the $offset and $limit variables and limit the number of projects to be displayed on first page load.

If the request is an Ajax request, the code within the braces is executed:

// convert limit and offset values to integer
$offset = intval(get('offset'));
$limit  = intval(get('limit'));

// limit projects using offset and limit values
$projects = $projects->offset($offset)->limit($limit);

// check if there are more projects left
$more = $count > $offset + $limit;

We first convert the values for offset and limit to integer. Then we apply those values to the offset() and limit() methods we call on $projects. In the last step, we check if the number of projects is still greater than the value of $offset plus $limit and depending on the result, we set$moretotrueorfalse`.

At the end of the controller, we return all variables so that they can be used by the template(s).

The JSON template

Now we create a second, content specific template for the JSON representation: projects.json.php. Let's take a look at the file:

<!-- /site/templates/projects.json.php -->
<?php

$html = '';

foreach($projects as $project) {

  // reuse the project snippet to create the HTML for each project
  // we need to set the third parameter to true, to return the
  // snippet content instead of echoing it
  $html .= snippet('project', compact('project'), true);

}

// add $html and $more to the $data array
$data['html'] = $html;
$data['more'] = $more;

// JSON encode the $data array
echo json_encode($data);

With this template set up, we can now make a call to http://example.com/projects.json in our Javascript code and the template will echo the JSON encoded data. But let's go through this in a little bit more detail.

First, we define a variable $html as an empty string. We then loop through the projects returned from the controller and add the HTML/PHP code for each project to the $html variable.

Next, the $html and $more variables are added to the $data array. And finally, we json_encode() the $data array, so that the data can be handled by our JavaScript code.

The JavaScript

To make our example work, we now have to create the JavaScript code (jQuery in this case).

// assets/js/script.js
$(function(){

  var element = $('.projects');
  var url     = element.data('page') + '.json';
  var limit   = parseInt(element.data('limit'));
  var offset  = limit;

  $('.load-more').on('click', function(e) {

    $.get(url, {limit: limit, offset: offset}, function(data) {

      if(data.more === false) {
        $('.load-more').hide();
      }

      element.children().last().after(data.html);

      offset += limit;

    });

  });

});

Let's go through this step by step:

We define a couple of variables that we will need later in the code.
```
 var element = $('.projects');
 var url     = element.data('page') + '.json';
 var limit   = parseInt(element.data('limit'));
 var offset  = limit;
```
We get the limit and the base part of the url variables from the data attributes we defined in the projects.php template above. Note that we add the json suffix to the URL, so that our JSON content representation will be fetched instead of the standard template.

Note: When using this code on your homepage, add a slash to value of the url variable: var url = element.data('page') + '/.json';
We add the event listener, which is triggered when the load-more button is clicked.
```
 $('.load-more').on('click', function(e) {

 });
```
The function contains the Ajax call:
```
 $.get(url, {limit: limit, offset: offset}, function(data) {

   if(data.more === false) {
     $('.load-more').hide();
   }

   element.children().last().after(data.html);

   offset += limit;

 });
```
With the Ajax request, we send the values for limit and offset to the project.php controller. If the GET request was successful, we append the HTML to the last child element of the .projects container:
```
 element.children().last().after(data.html);
```
We hide the button if there are no more projects left:
```
 if(data.more === false) {
   $('.load-more').hide();
 }
```
Finally, we increase the offset by the value of limit.
```
 offset += limit;
```

We are almost there. Now let's not forget to add jQuery and our script file to our footer.

<!-- /site/snippets/footer.php -->
<?php
  echo js([
    'assets/js/jquery.min.js',
    'assets/js/script.js'
  ]);
?>

Note that we include a local copy of jQuery in this example. As an alternative, you can load it from a CDN. Or rewrite to code to use vanilla JavaScript instead of jQuery, of course.

If Javascript is not available…

Depending on your use case, you may want to either hide the button if JavaScript is not available, or provide a fallback with a link to the complete list of projects.

Download files

The complete set of files (except for the jQuery library) for this tutorial can be found in the Cookbook repo.

For testing, you can add the files from each subfolder into the corresponding folders of a Kirby Starterkit or Plainkit.

We hope you enjoyed this tutorial. You can leave your feedback in the forum or on GitHub.