Implementing hook_tokens() for token replacementsfor Drupal 8 , 9 , 10 , and 11

Building upon the previous lesson where we defined custom tokens using hook_token_info(), this tutorial will guide you through implementing hook_tokens() in Drupal. By doing so, you will be able to replace these tokens with dynamic data, making your modules responsive to user context and cornerstones of customized content.

Understanding hook_tokens()

The hook_tokens() function is essential for specifying how tokens should be replaced at runtime with real values. This function intercepts tokens you defined and provides the actual data that should replace these placeholders when they are encountered in content or configuration.

Example Scenario

Let's continue with our hypothetical module, example_token, which defines user-related tokens. We'll now implement logic to substitute these tokens with user data, such as their username and email address.

Implementing hook_tokens()

Below is an example implementation of the hook_tokens() function:

<?php
/**
 * Implements hook_tokens().
 */
function example_token_tokens($type, $tokens, array $data, array $options, BubbleableMetadata $bubbleable_metadata) {
    $replacements = [];

    if ($type == 'example') {
        $current_user = \Drupal::currentUser();

        foreach ($tokens as $name => $original) {
            switch ($name) {
                case 'username':
                    $replacements[$original] = $current_user->getDisplayName();
                    break;

                case 'user_email':
                    $replacements[$original] = $current_user->getEmail();
                    break;
            }
        }
    }

    return $replacements;
}
?>

Breaking Down the Implementation

• Token Type Verification: The function checks if the $type variable matches the token type you're handling (e.g., example).
• Iterating Tokens: Loop through each token passed to the function in the $tokens array.
• Handling Specific Tokens: Use a switch-case structure to define the replacement for each specific token. Here, $current_user->getDisplayName() and $current_user->getEmail() fetch the current user's name and email for replacement.
• Output: Store replacements in the $replacements array, where the key corresponds to the original token, and return this array.

Testing Your Token Replacements

To ensure your tokens are functioning correctly, test them in contexts that support tokens, such as content types or custom blocks, as follows:

• Create a block with a body text like: "Hello [example:username], your email is [example:user_email]".
• Check that after saving and rendering the block, the tokens are replaced by your actual username and email address.

Refining Performance with Bubbleable Metadata

Bubbles ensure automatic handling of cacheability metadata for replacements. Drupal manages cache contexts, tags, and max-age via the passed $bubbleable_metadata variable, minimizing the developer's need for manual cache management while maintaining efficient caching strategies.

Best Practices

• Consistency: Ensure tokens are consistently defined and replaced across all relevant contexts to avoid unexpected behavior.
• Security: Validate that no sensitive information is inadvertently exposed through token replacements.
• Clarity: Well-documented tokens and replacement logic improve maintainability and user comprehension.

Conclusion

By implementing hook_tokens(), your custom tokens in Drupal are brought to life, dynamically transforming placeholders into personalized content. Harnessing this feature helps craft enriched user experiences and responsive web applications.

Looking Forward

In the next lesson, we will explore how to replace tokens programmatically. This will further deepen your skills in managing dynamic content within complex Drupal environments. Join us as your journey in mastering Drupal's module development continues!