storybook/docs/writing-stories/args.md

title
Args

A story is a component with a set of arguments (props, slots, inputs, etc). “Args” are Storybook’s mechanism for defining those arguments as a first class entity that’s machine readable. This allows Storybook and its addons to live edit components. You do not need to change your underlying component code to use args.

When an arg’s value is changed, the component re-renders, allowing you to interact with components in Storybook’s UI via addons that affect args.

For a discussion on how and why to write stories with args, check the using args section. For details on how args work, read on.

Args object

The args object can be defined at the story and component level (see below). It is an object with string keys, where values can have any type that is allowed to be passed into a component in your framework.

Story args

To define the args of a single story, use the args CSF story key:

export const Primary = Story.bind({});
Primary.args = {
  primary: true,
  label: ‘Primary’,
}

TODO: ask dom/tom for clarity on the reuse link location

These args will only apply to the story for which they are attached, although you can reuse them via JavaScript object reuse:

export const PrimaryLongName = Story.bind({});
PrimaryLongName.args = {
  ...Primary.args,
  label: ‘Primary with a really long name’,
}

In the above example, we use the object spread feature of ES 2015.

Component args

You can also define args at the component level; such args will apply to all stories of the component unless they are overwritten. To do so, use the args key of the default CSF export:

import Button from ‘./Button’;
export default {
  title: “Button”,
  component: Button,
  args: {
    // Now all Button stories will be primary.
    primary: true,
  },
};

Args composition

You can separate the arguments to a story to compose in other stories. Here’s how args can be used in multiple stories for the same component.

const Primary = ButtonStory.bind({});
Primary.args = {
  primary: true,
  label: ‘Button’,
}

const Secondary = ButtonStory.bind({});
Secondary.args = {
  ...Primary.args,
  primary: false,
}

needs to be vetted with frontpage and gatsby

Note that if you are doing the above often, you may want to consider using component-level args.

Args are useful when writing stories for composite components that are assembled from other components. Composite components often pass their arguments unchanged to their child components, and similarly their stories can be compositions of their child components stories. With args, you can directly compose the arguments:

/// Page.stories.js

import Page from ‘./Page’;
import * as Header from './Header.stories';

export const default {
  component: Page,
  title: ‘Page’,
};

const Story = (args) => <Page {...args} />
export const LoggedIn = Story.bind({});
LoggedIn.args = {
  ...Header.LoggedIn.args,
};

Using args in addons

If you are writing an addon that wants to read or update args, use the useArgs hook exported by @storybook/api:

import { useArgs } from ‘@storybook/api’;
const [args, updateArgs] = useArgs();
// To update one or more args:
updateArgs({ key: ‘value’ });

parameters.passArgsFirst

In Storybook 6+, we pass the args as the first argument to the story function. The second argument is the “context” which contains things like the story parameters etc.

In Storybook 5 and before we passed the context as the first argument. If you’d like to revert to that functionality set the parameters.passArgsFirst parameter in .storybook/preview.js:

export const parameter = { passArgsFirst : false }.

Note that args is still available as a key on the context.