We will review the basic functional structure of the Behavior itself, as this format becomes the essential form of Drupals JavaScript integration and it is in our interest to know its parts first. Remember that whatever the style guideline we choose, we always need to comply with two fundamental guidelines: We are going to makechanges on the rendered HTML of our Drupal through our custom module, for which we must first assign a custom selector to the element we want to modify. 6- Drupal Behaviors. Browse other questions tagged, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site. In a previous section, we already saw how to run jQuery in our code. Actually, the #states property ends up being managed from the JavaScript library drupal.states available for loading as a dependency in the form core/drupal.states, which points to the path where the library /core/misc/states.js is located inside Drupal, although its not necessary to make an explicit load of it since the rendering system that manages the Render Arrays checks the existence of the property and if it is present, it directly assigns the JavaScript library. Drupal: adding autocomplete to textfield for custom content type. Then the logic is stored in a file (and can be reviewed, linted and cached on the client side), and only the settings to configure the logic in that file need to be generated on each request. You cannot use other keys as these will cause strict warnings. Defining a library In your theme or module's root directory create a *. We want to make it hard to make Drupal slow down, so this is why we don't offer a nice API for this since we don't want you to do it. And so, if we go in our test Drupal on the path: We will already have available the new image board obtained from the Unsplash API and built from a Drupal Behavior: Here you have available the complete code of the Behavior that we have just implemented: It was necessary, at least, to make a review on these knowledge areas where JavaScript is of indirect handling and execution. In form buttons: adding the class use-ajax-submit in the element declaration, we will make a call with Ajax. Here you can check it out the AJAX API in Drupal. By now, we just need to go to the PHP class file (The Controller) and modify the render array that is returned at the end, including the #attached property with our new library: Just after changed it, We will reinstall our custom module, clearing cache: We can see now from the Console of your browser the result of the execution of our first JavaScript code, just going to the declared route: Weve made our first interaction with JavaScript in Drupal! Drupal 8 introduced the Dynamic Page Cache, which caches rendered fragments of the page and improves performance for authenticated users. To do this we must declare the core/drupalSettings as a dependency of our JavaScript library. You can also download this basic custom module created for examples from my gitlab repository: gitlab.com/davidjguru/basic_custom_module, or doing git clone from the whole repository for custom modules: gitlab.com/davidjguru/drupal-custom-modules-examples. Lets see the next exercise. libraries. More info here. We want to extract data about the visitors identity in order to give them a more personal greeting. This documentation needs work. If using drupalSettings plus a JavaScript file is not an option, then you still have one option left: use hook_page_attachments(), where you add a new value to $page['#attached']['html_head'], which contains either a