The Masquerade module allows website admins to switch users and visit the website as that user. This is helpful for developers and site builders when trying to find out what a client might see when logged into the website. To create the unmasquerade programmatically use this:

if (
  \Drupal::moduleHandler()->moduleExists('masquerade') && 
  \Drupal::service('masquerade')->isMasquerading()
){
  $links['unmasquerade'] = [
    '#type' => 'link',
    '#title' => t('Unmasquerade'),
    '#url' => Url::fromRoute('masquerade.unmasquerade'),
    '#weight' => 1500,
  ];
}

Making a simple HTTP Get request in Drupal 8, 9 or 10 is super easy thanks to the Guzzle library. This library has been added to Drupal core a long time ago, and it replaced the much less powerful drupal_http_request() function. Let's see how to get some data from the Star Wars API:

use GuzzleHttp\Client;
use GuzzleHttp\Exception\RequestException;

$client = new Client();
$people = [];

try {
  $response = $client->get('https://swapi.dev/api/people');
  $result = json_decode($response->getBody(), TRUE);
  foreach($result['results'] as $item) {
    $people[] = $item['name']; 
  }
}
catch (RequestException $e) {
  // log exception
}

Guzzle can also be accessed through the http_client service and the helper method:

$client = \Drupal::httpClient();

Sending a POST request is also simple and easy.

public function sendOrder(OrderInterface $order) {
  try {
    $response = $this->httpClient->post($url, [
      'form_params' => $data,
    ]);
    $response_data = json_decode($response->getBody()->getContents(), TRUE);

    // do something with data
  }
  catch (RequestException $e) {
    // log exception
  }
}

If you want to log the exception don't use $e->getMessage() because the error message will be truncated. Instead, use this:

$e->getResponse()->getBody()->getContents();

You can also use Guzzle to send files. To send an image file you can do something like this:

try {
  $client = new Client(['headers' => ['X-Auth-Secret-Token' => 'my-secret-token']]);
  $options = [
    'multipart' => [
      [
        'Content-type' => 'multipart/form-data',
        'name' => 'image',
        'contents' => fopen($image->getFileUri(), 'r'),
        'filename' => basename($image->getFileUri()),
      ],
    ],
  ];
  $response = $client->post($api_base_url . 'api/v1/images', $options);
}
catch (\Exception $e) {
  // log exception
}

In this case, the $image variable is an instance of Drupal\file\Entity\File class.

Let's say that a contrib module is showing a message like this: Your message has been created, and you want to change it to something like this: Message created. To do this you don't have to hack the contrib module, you can use the hook_preprocess_HOOK() to alter the message.

/**
 * Implements hook_preprocess_HOOK().
 */
function MY_MODULE_preprocess_status_messages(&$variables) {
  if (isset($variables['message_list']['status'])){
    $status_messages = $variables['message_list']['status'];
    foreach($status_messages as $delta => $message) {
      if (strpos((string) $message, 'Your message has been created.') !== FALSE) {
        $variables['message_list']['status'][$delta] = t('Message created.');
      }
    }
  }
}

One way to alter the page title is to use hook_preprocess_HOOK() and then set the new page title depending on the current route name.

function MY_MODULE_preprocess_page_title(&$variables) {
  $route_name = \Drupal::routeMatch()->getRouteName();
  if ($route_name === 'entity.user.edit_form') {
    $variables['title'] = 'Edit My Account';
  }
}

This will only change the title in the Page title block. To actually change the <title> HTML tag you can use the following code snippet:

function MY_MODULE_preprocess_html(&$variables) {
  $route_name = \Drupal::routeMatch()->getRouteName();
  if ($route_name === 'entity.user.edit_form') {
    $variables['head_title']['title'] = t('Edit My Account')
  }
}

If you want to hide a field inside the Inline Entity Form you have to use the hook_inline_entity_form_entity_form_alter() hook – standard form alter hook won’t work. For example, to hide the status field you can do something like this:

/**
 * Implements hook_inline_entity_form_entity_form_alter().
 */
function MY_MODULE_inline_entity_form_entity_form_alter(&$entity_form, &$form_state) {
  if (in_array($entity_form['#entity_type'], ['YOUR_ENTITY_TYPE_1', 'YOUR_ENTITY_TYPE_2'])) {
    $entity_form['status']['#access'] = FALSE;
  }
}

Hiding the Add to Cart button in Drupal Commerce 2.x is easy. Just alter the commerce_order_item_add_to_cart_form form, and set the disabled property of the button to true.

use Drupal\Core\Form\FormStateInterface;

function MY_MODULE_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  if (strpos($form_id, 'commerce_order_item_add_to_cart_form') !== FALSE) {
    $product = $form_state->getFormObject()->getEntity()->getPurchasedEntity()->getProduct();
    
    $flag_service = \Drupal::service('flag');
    $flag = $flag_service->getFlagById('sold_out');
    $flagging = $flag_service->getFlagging($flag, $product);

    if ($flagging !== NULL ) {
      $form['actions']['submit']['#value'] = t('Out of stock');
      $form['actions']['submit']['#disabled'] = TRUE;
    }
  }
}

If you have only one payment method, then Drupal Commerce 2.x will hide it. We can change that behavior in the form alter hook.

use Drupal\Core\Form\FormStateInterface;

function MY_MODULE_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  if ($form_id == 'commerce_checkout_flow_multistep_default') {
    if (isset($form['payment_information']['payment_method']['#access'])) {
      $form['payment_information']['payment_method']['#access'] = TRUE;
    }
  }
}

If you are using the UI you can add a Recaptcha only to the entire checkout form, and that usually is not what you want. Fortunately, adding a Recaptcha to a certain step is easy:

use Drupal\Core\Form\FormStateInterface;

function MY_MODULE_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  if ($form_id == 'commerce_checkout_flow_multistep_default' && $form['#step_id'] == 'order_information') {
    $form['captcha'] = [
      '#type' => 'captcha',
      '#captcha_type' => 'recaptcha/reCAPTCHA',
    ];
  }
}

In some cases, you may want to add a role when a new user is created regardless of how the user is created (UI, GraphQL, Rest API, or something else). The hook_ENTITY_TYPE_presave() hook is perfect for this.

use Drupal\user\UserInterface;

function MY_MODULE_user_presave(UserInterface $user) {
  if ($user->isNew() && !$user->hasRole('frontend_app')) {
    $user->addRole('frontend_app');
  }
}

Adding a menu link to some existing menu programmatically (for example in an update hook) is something I have to do fairly often. Here's how you can add a new menu link to the main menu:

use Drupal\menu_link_content\Entity\MenuLinkContent;

function MY_MODULE_update_8001() {
  MenuLinkContent::create([
    'title' => 'About',
    'link' => ['uri' => 'internal:/about'],
    'menu_name' => 'main',
    'weight' => -50,
  ])->save();
}

And if you want to add a submenu link you first have to load the parent link and then create a submenu link:

use Drupal\menu_link_content\Entity\MenuLinkContent;

function MY_MODULE_update_8001() {
  $menu_link_parents = \Drupal::entityTypeManager()
    ->getStorage('menu_link_content')
    ->loadByProperties([
      'title' => 'Dashboard',
      'menu_name' => 'main',
    ]);

  $menu_link_parent = reset($menu_link_parents);

  if ($menu_link_parent) {
    MenuLinkContent::create([
      'title' => 'Add tasks',
      'link' => ['uri' => 'internal:/add-task'],
      'menu_name' => 'main',
      'weight' => -50,
      'parent' => $menu_link_parent->getPluginId(),
    ])->save();
  }
}