The way of handling javascript and css is different from drupal 7. This snippet shows how to do it.
When you give users the permission to administer users, there is a security implication in that users with this permission can add the role 'administrator' role to any user.

Block access is a powerful way to show or hide content in some contexts. Instead of using contrib modules, this is very easy in small pieces of custom code. The following code prevents access to a block based on a subscription field in the user object.

The following code shows how to create a custom form in the drupal back-end and how to save custom config defined in your custom module. Powerful stuff and very flexible.

You can update custom config with a settings form you build. 
In a custom module *custom_mailing* add a file called *custom_mailing.routing.yml* add the following route:

Custom formatters are great to get precise control over your field output. But I ran into something difficult when trying to output the description of a file field.
In a node teaser or full view mode it is for front-end purposes needed to know if an image is available. This snippet takes care of it.
When using twig, sometimes you would like to know whether the view has results or not. This snippet shows you how.
How do you get the base url of a drupal 8 website programmatically?