Drupal 8 - adding body class based on taxonomy term or other - drupal

Question

Building a site in Drupal 8, using classy subtheme. Run into a puzzling theming issue - adding body class to html.html.twig based on a taxonomy term on that node.
Themers use this to customize page display, in my case using it to define a few sections of my site so I can change color and format.
I have tried some preprocess functions I saw on google but to no result.
Has anyone else run into and solved this issue?

Answer 1

Use this to get all fields of the node and check for whatever you need:
\Drupal::service('current_route_match')->getParameter('node')->toArray();
In your .theme file you can use the html preprocess hook:
function your_theme_preprocess_html(&$variables) {
$body_classes = [];
$nodeFields = \Drupal::service('current_route_match')->getParameter('node')->toArray();
// if something, then set $body_classes to something.
$variables['attributes']['class'] += $body_classes;
}
And then in your html twig template add the attributes to the body element:
<body{{ attributes }}>
Hope this helps.

Answer 2

With the answer of Frank Drebin I get a PHP fatal error (Unsupported operand types) with the "+=" operand. If you want to add the node ID and node type to your body class, you can use this code for example:
// Add the node ID and node type to the body class
$body_classes = [];
$nodeFields = \Drupal::service('current_route_match')->getParameter('node')->toArray();
if (is_array($nodeFields) && count($nodeFields) > 0) {
if (isset($nodeFields['nid'])) {
$body_classes[] = 'node-' . $nodeFields['nid'][0]['value'];
}
if (isset($nodeFields['type'])) {
$body_classes[] = $nodeFields['type'][0]['target_id'];
}
}
$variables['attributes']['class'] = $body_classes;