Writing your stories in TypeScript makes you more productive. You don't have to jump between files to look up component props. Your code editor will alert you about missing required props and even autocomplete prop values, just like when using your components within your app. Plus, Storybook infers those component types to auto-generate the Controls table.
Storybook has built-in TypeScript support, so you can get started with zero configuration required.
Typing stories with Meta and StoryObj
When writing stories, there are two aspects that are helpful to type. The first is the component meta, which describes and configures the component and its stories. In a CSF file, this is the default export. The second is the stories themselves.
Storybook provides utility types for each of these, named Meta and StoryObj. Here's an example CSF file using those types:
Props type parameter
Meta and StoryObj types are both generics, so you can provide them with an optional prop type parameter for the component type or the component's props type (e.g., the typeof Button portion of Meta<typeof Button>). By doing so, TypeScript will prevent you from defining an invalid arg, and all decorators, play functions, or loaders will type their function arguments.
The example above passes a component type. See Typing custom args for an example of passing a props type.
Using satisfies for better type safety
We are not yet able to provide additional type safety using the satisfies operator with Angular and Web components.
More info
Both Angular and Web components utilize a class plus decorator approach. The decorators provide runtime metadata, but do not offer metadata at compile time.
As a result, it appears impossible to determine if a property in the class is a required property or an optional property (but non-nullable due to a default value) or a non-nullable internal state variable.
For more information, please refer to this discussion.
If you are using TypeScript 4.9+, you can take advantage of the new satisfies operator to get stricter type checking. Now you will receive type errors for missing required args, not just invalid ones.
Using satisfies to apply a story's type helps maintain type safety when sharing a play function across stories. Without it, TypeScript will throw an error that the play function may be undefined. The satisfies operator enables TypeScript to infer whether the play function is defined or not.
Finally, use of satisfies allows you to pass typeof meta to the StoryObj generic. This informs TypeScript of the connection between the meta and StoryObj types, which allows it to infer the args type from the meta type. In other words, TypeScript will understand that args can be defined both at the story and meta level and won't throw an error when a required arg is defined at the meta level, but not at the story level.
Typing custom args
Sometimes stories need to define args that aren’t included in the component's props. For this case, you can use an intersection type to combine a component's props type and your custom args' type. For example, here's how you could use a footer arg to populate a child component:
Vue specific tips
Vue has excellent support for TypeScript, and we have done our utmost to take advantage of that in the stories files. For example, consider the following strongly typed Vue 3 single file component (SFC):
You can type check SFC files with vue-tsc and get editor support in VSCode by installing the Vue Language Features (Volar) and TypeScript Vue Plugin extensions.
This setup will add type support for *.vue imports to your *.stories.ts files, providing the same type safety and autocomplete features.
Svelte specific tips
Svelte offers excellent TypeScript support for .svelte files. For example, consider the following component. You can run type checks using svelte-check and add VSCode editor support with the Svelte for VSCode extension.
The same setup works with Svelte stories files too, providing both type safety and autocompletion.
