React Components

Component Guidelines

•Named exports only: export const MyComponent = ... (no default exports)
•Plain arrow functions: Don't type with React.FC
•No spread props in GraphQL wrappers: List all props individually for type safety

tsx

interface MyComponentProps {
  title: MessageFormat;
  onSubmit: () => void;
}

export const MyComponent = ({ title, onSubmit }: MyComponentProps) => {
  // ...
};

UI Components (no GraphQL)

Simple structure—see example: commons-packages/frontend/shared/example-ui-component/

tsx

interface ExampleUiComponentProps {
  description?: MessageFormat;
  onSubmitClick: () => void;
  title: MessageFormat;
}

export const ExampleUiComponent = ({ description, onSubmitClick, title }: ExampleUiComponentProps) => {
  // Component implementation
};

GraphQL Components

Separate into two components:

•UI sub-component (MyComponentUI): Renders UI, receives data as props
•GraphQL wrapper (MyComponent): Fetches data, passes to UI

See example: commons-packages/frontend/shared/example-graphql-component/

tsx

// UI sub-component
interface MyComponentUIProps extends MyComponentBaseProps {
  error?: ApolloError;
  isLoading?: boolean;
  data?: GetDataQuery['data'];
}

export const MyComponentUI = ({ error, isLoading, data }: MyComponentUIProps) => {
  if (isLoading) return <Spinner />;
  if (error) return <ErrorComponent error={error} />;
  return (/* render UI */);
};

// GraphQL wrapper
export const MyComponent = ({ id }: MyComponentProps) => {
  const { data, loading, error } = useGetDataQuery({ variables: { id } });

  return (
    <MyComponentUI
      isLoading={loading}
      error={error}
      data={data?.data}
    />
  );
};

Custom Hooks

•Prefix with use: useMyHook
•Return typed objects or tuples
•Place in hooks/ directory or co-locate with component

tsx

interface UseMyHookResult {
  value: string;
  setValue: (v: string) => void;
  isLoading: boolean;
}

export const useMyHook = (initialValue: string): UseMyHookResult => {
  // ...
};

Internationalization

Use MessageFormat for text. Render with useFormatMessage from Commonplace (not useIntl from react-intl):

tsx

import { Text, useFormatMessage } from '@commons/frontend/shared/commonplace';

const Component = ({ pageNumber }: { pageNumber: number }) => {
  const formatMessage = useFormatMessage();
  const nextText = formatMessage({ id: 'shared.next' });
  return <Text text={`${nextText}: ${pageNumber}`} />;
};

Testing

Import from test-utils

tsx

import { render } from '@commons/frontend/rtlTests/test-utils';

This wraps components with necessary providers (IntlProvider, MockedProvider, AppStateProvider, Router).

Two Approaches for GraphQL Components

•
Test UI sub-component directly — pass props without mocks:
tsx
```
render(<MyComponentUI data={mockData} isLoading={false} />);
```

•

Use GraphQL mocks — test full wrapper:

tsx

render(<MyComponent id="123" />, { customMocks: [myMock] });

See examples: commons-packages/frontend/shared/example-graphql-component/__tests__/

File Structure

Co-locate related files:

code

my-component/
├── my-component.tsx
├── my-component.graphql
├── my-component.css (or .module.css)
└── __tests__/
    └── my-component.spec.tsx