A decorator is a way to wrap a story in extra “rendering” functionality. Many addons define decorators to augment your stories with extra rendering or gather details about how your story renders.

When writing stories, decorators are typically used to wrap stories with extra markup or context mocking.

Wrap stories with extra markup

Some components require a “harness” to render in a useful way. For instance, if a component runs right up to its edges, you might want to space it inside Storybook. Use a decorator to add spacing for all stories of the component.

Story without padding

Story with padding

“Context” for mocking

Framework-specific libraries (e.g., Styled Components, Fortawesome for Vue) may require additional configuration to render correctly in Storybook.

For example, if you're working with Styled Components and your components use a theme, add a single global decorator to .storybook/preview.js to provide it. Or with Vue, extend Storybook's application and register your library:

In the example above, the values provided are hardcoded. Still, you may want to vary them, either on a per-story basis (i.e., if the values you're providing are relevant to a specific story) or in a user-controlled way (e.g., provide a theme switcher or a different set of icons).

The second argument to a decorator function is the story context which in particular contains the keys:

  • args - the story arguments. You can use some args in your decorators and drop them in the story implementation itself.
  • argTypes- Storybook's argTypes allow you to customize and fine-tune your stories args.
  • globals - Storybook-wide globals. In particular you can use the toolbars feature to allow you to change these values using Storybook’s UI.
  • hooks - Storybook's API hooks (e.g., useArgs).
  • parameters- the story's static metadata, most commonly used to control Storybook's behavior of features and addons.
  • viewMode- Storybook's current active window (e.g., canvas, docs).
💡 This pattern can also be applied to your own stories. Some of Storybook's supported frameworks already use it (e.g., vue 2).

Using decorators to provide data

If your components are “connected” and require side-loaded data to render, you can use decorators to provide that data in a mocked way without having to refactor your components to take that data as an arg. There are several techniques to achieve this. Depending on exactly how you are loading that data -- read more in the building pages in Storybook section.

Story decorators

To define a decorator for a single story, use the decorators key on a named export:

It is useful to ensure that the story remains a “pure” rendering of the component under test, and any extra HTML or components don't pollute that. In particular the Source docblock works best when you do this.

Component decorators

To define a decorator for all stories of a component, use the decorators key of the default CSF export:

Global decorators

We can also set a decorator for all stories via the decorators export of your .storybook/preview.js file (this is the file where you configure all stories):

Decorator inheritance

Like parameters, decorators can be defined globally, at the component level, and for a single story (as we’ve seen).

All decorators relevant to a story will run in the following order once the story renders:

  • Global decorators, in the order they are defined
  • Component decorators, in the order they are defined
  • Story decorators, in the order they are defined.
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