What are Transformers?

Transformers are a way to document more complex arguments in your Storybook stories.

The big problem with complex arguments is that they are not easily documented in the Storybook UI. Storybook only supports basic types like string, number, boolean, etc.

The Storybook extension also automaticall creates Selects for PHP enums and sets the Storybook type to select. For DateTime, DateTimeImmutable and DateTimeInterface it creates a date picker.

for all other complex Types we need a Transformer to convert basic types to a more complex type.

TypeTransformer

The TYPO3 object \TYPO3\CMS\Core\Http\Uri is one of the complex types. As Storybook sends all Objects from JS-Browserland via JSON to PHP, we dont get the native PHP object.

EXT:storybook provides a Transformer for the \TYPO3\CMS\Core\Http\Uri object.

it looks like this:

...

use Andersundsehr\Storybook\Transformer\Attribute\TypeTransformer;
use TYPO3\CMS\Core\Http\Uri;

class ...
{
    #[TypeTransformer(priority: 100)]
    public function uri(string $url): Uri
    {
        return new Uri($url);
    }
}
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As you can see the Transformers can be really simple. A TypeTransformer is any Function on any Service that has the #[TypeTransformer] attribute. It can take any number of arguments, the argument types need to be basic types like string, int, bool, etc. or DateTime, DateTimeImmutable, DateTimeInterface, or any UnitEnum.

The return type of the function is the complex type that you want to transform to.

All types are required. As that information is used to generate the Storybook UI Controls.

priority of TypeTransformers

You can order the TypeTransformers by priority, highest number wins.

To debug the TypeTransformers used you can take a look in the TYPO3 Backend Module System -> Configuration and select the EXT:storybook TypeTransformers Configuration. There you can see all registered TypeTransformers and their priorities.

Per Argument Transformers

Sometimes we don't want to transform the arguments by type but by the argument name.

For that we can define a *.transformers.php file in the same directory as the *.html file.

Components/TransformerExample/TransformerExample.transformer.php 
<?php

use Andersundsehr\Storybook\Transformer\ArgumentTransformers;
use TYPO3\CMS\Core\Http\Uri;
use TYPO3\CMS\Core\Type\ContextualFeedbackSeverity;

return new ArgumentTransformers(
    // uri: uses the TypeTransformer automatically.
    websocket: fn(string $url): Uri => (new Uri($url))->withScheme('wss'),
    contextIcon: fn(ContextualFeedbackSeverity $severity): string => $severity->getIconIdentifier(),
    // TODO add more examples (eg. SysFile/SysFileReference, ContentBlockData)
    combineUri: fn(string $host, string $path, string $query = '', string $fragment = '', string $scheme = 'https'): Uri => new Uri(
        $scheme . '://' . $host . '/' . $path . '?' . $query . '#' . $fragment
    ),
    transformerWithoutArguments: fn(): Uri => new Uri('https://storybook.andersundsehr.com'),
);
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