Same name in other branches

1. 7.x modules/system/system.api.php \hook_form_FORM_ID_alter()
2. 9 core/lib/Drupal/Core/Form/form.api.php \hook_form_FORM_ID_alter()
3. 10 core/lib/Drupal/Core/Form/form.api.php \hook_form_FORM_ID_alter()
4. 11.x core/lib/Drupal/Core/Form/form.api.php \hook_form_FORM_ID_alter()

Provide a form-specific alteration instead of the global hook_form_alter().

Implementations are responsible for adding cache contexts/tags/max-age as needed. See https://www.drupal.org/docs/8/api/cache-api/cache-api.

Modules can implement hook_form_FORM_ID_alter() to modify a specific form, rather than implementing hook_form_alter() and checking the form ID, or using long switch statements to alter multiple forms.

Form alter hooks are called in the following order: hook_form_alter(), hook_form_BASE_FORM_ID_alter(), hook_form_FORM_ID_alter(). See hook_form_alter() for more details.

Parameters

$form: Nested array of form elements that comprise the form.

$form_state: The current state of the form. The arguments that \Drupal::formBuilder()->getForm() was originally called with are available in the array $form_state->getBuildInfo()['args'].

$form_id: String representing the name of the form itself. Typically this is the name of the function that generated the form.

See also

hook_form_alter()

hook_form_BASE_FORM_ID_alter()

\Drupal\Core\Form\FormBuilderInterface::prepareForm()

Related topics

84 functions implement hook_form_FORM_ID_alter()

Note: this list is generated by pattern matching, so it may include some functions that are not actually implementations of this hook.

automated_cron_form_system_cron_settings_alter in core/modules/automated_cron/automated_cron.module

Implements hook_form_FORM_ID_alter() for the system_cron_settings() form.

block_form_form_test_alter_form_alter in core/modules/system/tests/modules/form_test/form_test.module

Implements hook_form_FORM_ID_alter() on behalf of block.module.

book_form_node_confirm_form_alter in core/modules/book/book.module

Implements hook_form_BASE_FORM_ID_alter() for \Drupal\node\Form\NodeDeleteForm.

book_form_node_form_alter in core/modules/book/book.module

Implements hook_form_BASE_FORM_ID_alter() for \Drupal\node\NodeForm.

claro_form_media_form_alter in core/themes/claro/claro.theme

Implements hook_form_BASE_FORM_ID_alter() for \Drupal\media\MediaForm.

... See full list

File

core/lib/Drupal/Core/Form/form.api.php, line 245

Code

function hook_form_FORM_ID_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
    // Modification for the form with the given form ID goes here. For example, if
    // FORM_ID is "user_register_form" this code would run only on the user
    // registration form.
    // Add a checkbox to registration form about agreeing to terms of use.
    $form['terms_of_use'] = [
        '#type' => 'checkbox',
        '#title' => t("I agree with the website's terms and conditions."),
        '#required' => TRUE,
    ];
}

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