How to include a function in angular storybook args?

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05-10-2024

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Passing Functions as Arguments in Angular Storybook: A Developer's Guide

Storybook is an invaluable tool for Angular developers, allowing them to create interactive and isolated components for testing and documentation. However, when working with complex components that require dynamic behavior, passing functions as arguments in Storybook's args can seem tricky. This article will demystify the process, providing a clear explanation and practical examples.

The Problem: Dynamic Behavior Beyond Static Data

Imagine building a complex component, such as a "User Profile" component. You want to test various user actions, like updating profile information or toggling settings. Simply passing static data in args won't suffice for this. You need to include functions that simulate these user actions, allowing your component to behave dynamically within the Storybook environment.

Code Example: Static Data vs. Functional Arguments

Original Code (Static Data):

// user-profile.component.ts
@Component({
  selector: 'app-user-profile',
  template: `
    <div>
      <p>Name: {{user.name}}</p>
      <button (click)="updateUser()">Update Profile</button>
    </div>
  `,
})
export class UserProfileComponent {
  user = { name: 'John Doe' };

  updateUser() {
    // ...update logic here
  }
}

// user-profile.stories.ts
import { UserProfileComponent } from './user-profile.component';

export default {
  title: 'Components/UserProfile',
  component: UserProfileComponent,
  args: {
    user: { name: 'John Doe' }
  }
};

export const Primary = {};

In this example, the updateUser function is defined within the component and triggered on button click. However, within the Storybook args, we are only providing static data (user) and not a function.

The Solution: Using actions and argTypes

Storybook provides the actions and argTypes capabilities to include functional arguments. Here's how to implement this:

Modified Code (Dynamic Behavior):

// user-profile.stories.ts
import { UserProfileComponent } from './user-profile.component';
import { action } from '@storybook/addon-actions';

export default {
  title: 'Components/UserProfile',
  component: UserProfileComponent,
  argTypes: {
    updateUser: { action: 'updateUser' }
  },
  args: {
    user: { name: 'John Doe' },
    updateUser: action('updateUser')
  }
};

export const Primary = {};

Explanation:

1. argTypes: We define updateUser as an argType with the action property set to 'updateUser'. This informs Storybook that this argument is a function and should be logged using the actions addon.
2. args: In our args, we use the action function from @storybook/addon-actions to create a function named 'updateUser'. This function will be passed to the UserProfileComponent when the story is rendered.

Now, whenever the "Update Profile" button is clicked within the Storybook environment, the updateUser function will be triggered and logged in the Storybook actions panel. This allows us to test the dynamic behavior of the component.

Further Enhancements: Providing Custom Function Logic

You can create even more complex interactions by defining custom functions in the args and passing them to the component. For instance, you could create a function that simulates a user input, triggering a specific action in the component:

// user-profile.stories.ts
import { UserProfileComponent } from './user-profile.component';
import { action } from '@storybook/addon-actions';

export default {
  title: 'Components/UserProfile',
  component: UserProfileComponent,
  argTypes: {
    onChange: { action: 'onChange' }
  },
  args: {
    user: { name: 'John Doe' },
    onChange: (newValue) => action('onChange')(newValue)
  }
};

export const Primary = {};

In this example, onChange takes the new input value and triggers the onChange action, allowing you to observe the updated value in the Storybook actions panel.

Conclusion: Unleash Dynamic Behavior in Storybook

By leveraging actions and argTypes, you can seamlessly include functions as arguments in your Angular Storybook components. This empowers you to test complex scenarios, simulate user interactions, and gain a deeper understanding of your component's dynamic behavior. Experiment with different scenarios and use these techniques to enhance your development process and deliver robust, interactive components.