Example Kirby 3 recipe for creating a JSON Feed representation of a page with custom route

kirby__config.php

<?php
  // Kirby site config file
  // site/config/config.php
  return [
    'routes' => [
      [
      // This sets up two different URLs as an array that will 
      // return the JSON Feed representation of a page in Kirby
      'pattern' => ['feed', 'some-other-path/feed'],
      'action' => function() {
        return page('some-page-name')->render([],'json');
      },
      'method' => 'GET'
      ],
    ],
  ]

some_page_name.json.php

<?php
  // JSON representation template for a page
  // called "some_page_name
  // in site/templates/some_page_name.json.php

  // I found this line was necessary despite the route
  // having a json response type defined - YMMV
  $kirby->response()->json();

  // Set up some variables to handle the boilerplate
  // info for the feed
  $feed_title = "Title of the page, potentially pull from $page object";
  $feed_description = "Description of the page content";
  $feed_icon = "URL to an image";
  $feed_favicon = "URL to a favicon image, ideally transparent PNG 64x64 minimum";
  $feed_author = "Author full name";
  $feed_author_image = "URL to an image, could be the same as the $feed_icon variable above";

  // I use a controller to do the initial legwork of collecting an array
  // of children from the page, returned here as $some_page_children with a limit applied
  $feed = $some_page_children->limit(10);

  // Loop through each of the items in the array returned
  // and create the set of feed items
  // see also: https://jsonfeed.org/version/1.1 for details
  // but these are the basic required items + the optional date item
  foreach($feed as $item) {
  $entries[] = [
    'id' => (string)$item->indexOf(),
    'url'   => (string)$item->url(),
    'title' => (string)$item->title(),
    'content_html'  => (string)$item->text()->kirbytext(),
    'date_published'  => (string)$item->date()
  ];
}

$feed_json = [
  'version' => 'https://jsonfeed.org/version/1',
  'title' => (string)$feed_title,
  'description' => (string)$feed_description,
  'home_page_url' => (string)$site->url(),
  'feed_url' => (string)$page->url() . '.json',
  'icon' => (string)$feed_icon,
  'favicon' => (string)$feed_favicon,
  'authors' => [
    'name' => (string)$feed_author,
    'url' => (string)$site->url(),
    'avatar' => (string)$feed_author_image
  ],
  'language' => 'en-us',
  'items' => $entries
];

echo json_encode($feed_json);

some_page_name.php

<?php
  // Simple controller for the page
  // in site/controllers/some_page_name.php

  return function ($page) {
    // Get all articles
    $some_page_children = $page->children()->listed()->sortBy('date','desc');
    return [
      'some_page_children' => $some_page_children
    ];
  };

some_page_name_alternate.json.php

<?php
  // JSON representation template for a page
  // called "some_page_name
  // in site/templates/some_page_name.json.php
  // Alternate version from above

  // I found this line was necessary despite the route
  // having a json response type defined - YMMV
  $kirby->response()->json();

  // Set up some variables to handle the boilerplate
  // info for the feed
  $feed_title = "Title of the page, potentially pull from $page object";
  $feed_description = "Description of the page content";
  $feed_icon = "URL to an image";
  $feed_favicon = "URL to a favicon image, ideally transparent PNG 64x64 minimum";
  $feed_author = "Author full name";
  $feed_author_image = "URL to an image, could be the same as the $feed_icon variable above";
  $feed_reply_link_open = "<hr><p><a href='mailto:feedback@domain.com?subject=Response to ";
  $feed_reply_link_close = "'>Reply via e-mail</a></p>";

  // I use a controller to do the initial legwork of collecting an array
  // of children from the page, returned here as $some_page_children with a limit applied
  $feed = $some_page_children->limit(10);

  // Loop through each of the items in the array returned
  // and create the set of feed items
  // see also: https://jsonfeed.org/version/1.1 for details
  // but these are the basic required items + the optional date item
  foreach($feed as $item) {
  $entries[] = [
    'id' => (string)$item->indexOf(),
    'url'   => (string)$item->url(),
    'title' => (string)$item->title(),
    'content_html'  => (string)$article->text()->kirbytext() . $feed_reply_link_open . $article->title()->html() . $feed_reply_link_close,
    'date_published'  => (string)$item->date()
  ];
}

$feed_json = [
  'version' => 'https://jsonfeed.org/version/1',
  'title' => (string)$feed_title,
  'description' => (string)$feed_description,
  'home_page_url' => (string)$site->url(),
  'feed_url' => (string)$page->url() . '.json',
  'icon' => (string)$feed_icon,
  'favicon' => (string)$feed_favicon,
  'authors' => [
    'name' => (string)$feed_author,
    'url' => (string)$site->url(),
    'avatar' => (string)$feed_author_image
  ],
  'language' => 'en-us',
  'items' => $entries
];

echo json_encode($feed_json);