Use case:

I have a custom block:

 * Provides a 'Hello' Block
 * @Block(
 *   id = "my",
 *   admin_label = @Translation("My Block"),
 * )
class MyBlock extends BlockBase {

   * {@inheritdoc}
  public function build() {

    $build = array(
      '#markup' => 'SOME WEIRD ADS HTML HERE'


    return $build;

Is there a way to add inline javascript to the end of the page just when this block is rendered anywhere (in theme or panel page)?

  • The answer is actually no, not really. You can ad it right there as inline within the #markup (you might need to create a safe string with Markup::create). But what you can do for example is combine a library with drupalSettings to instrumentalize it. And then loop over ad positions in a drupal behavior based on the settings. That's what we're doing. – Berdir Aug 10 '16 at 20:14

You just use the following code.

$build = [
  '#markup' => 'SOME WEIRD ADS HTML HERE',
  '#attached' => [
    'library' => ['mymodule/mylibrary'],

Follow Adding stylesheets (CSS) and JavaScript (JS) to a Drupal 8 module to learn how to define a library for Drupal 8, and keep in mind that, by default, JavaScript files are added to the footer, as explained in LibraryDiscoveryParser::parseLibraryInfo().

By default, JavaScript files are included in the footer.

Also, #markup is filtered out, as explained in Render API overview.

#markup: Specifies that the array provides HTML markup directly. Unless the markup is very simple, such as an explanation in a paragraph tag, it is normally preferable to use #theme or #type instead, so that the theme can customize the markup. Note that the value is passed through \Drupal\Component\Utility\Xss::filterAdmin(), which strips known XSS vectors while allowing a permissive list of HTML tags that are not XSS vectors. (For example, <script> and <style> are not allowed.) See \Drupal\Component\Utility\Xss::$adminTags for the list of tags that will be allowed. If your markup needs any of the tags that are not in this whitelist, then you can implement a theme hook and template file and/or an asset library. Alternatively, you can use the render array key #allowed_tags to alter which tags are filtered.

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