Frontend

Frontend Development (React/Redux)

Component Structure

Functional Components

• Use functional components with hooks (no class components)
• Prefer named exports over default exports
• Keep components focused and single-responsibility
• Extract complex logic into custom hooks

Component Folder Structure

Each component in its own directory under **/ComponentName:

ComponentName/
  ComponentName.tsx          # Main component
  ComponentName.styles.ts    # Styled-components styles (PascalCase)
  ComponentName.types.ts     # TypeScript interfaces
  ComponentName.spec.tsx     # Tests
  ComponentName.constants.ts # Constants
  ComponentName.story.tsx    # Storybook examples
  hooks/                     # Custom hooks
  components/                # Sub-components
  utils/                     # Utility functions

Props Interface

• Name as ComponentNameProps
• Use separate interfaces for complex prop objects
• Always use proper TypeScript types, never any

Imports Order in Components

1. External dependencies (react, redux, etc.) 2. Internal modules (aliases) 3. Local imports (types, constants, hooks) 4. Styles (always last: import { Container } from './Component.styles')

Barrel Files

Use barrel files (index.ts) only when exporting 3 or more items. Make sure exports appear in only one barrel file, not propagated up the chain.

Styled Components

We are migrating to styled-components (deprecating SCSS modules).

Encapsulate Styles in .styles.ts

Keep all component styles in dedicated .styles.ts files using styled-components. Use PascalCase for the filename to match the component name:

ComponentName/
  ComponentName.tsx
  ComponentName.styles.ts  # ✅ PascalCase
  # Not component-name.styles.ts ❌

Import Pattern

Keep all component styles in dedicated .style.ts files and import them with a namespace.

*CRITICAL: `import as S is reserved for local styles only** (e.g., from ComponentName.styles.ts`). When you need to use styled components from external components, create a local styles file that re-exports them.

✅ Good

// ComponentName.tsx
import * as S from './ComponentName.styles'

return (
  <S.Container>
    <S.Title>Title</S.Title>
    <S.Content>Content</S.Content>
  </S.Container>
)

// ComponentName.styles.ts (when re-exporting from external component)
export { ExternalStyledComponent } from '../ExternalComponent/ExternalComponent.styles'

❌ Bad

// ❌ BAD: Importing styled components directly from external component
import * as S from '../ExternalComponent/ExternalComponent.styles'

// ❌ BAD: Named imports instead of namespace
import { Container, Title, Content } from './Component.styles'

Use Layout Components Instead of div

Prefer `FlexGroup` over `div` when creating flex containers:

// ✅ GOOD: Use FlexGroup
import { FlexGroup } from 'uiSrc/components/base/layout/flex'

export const Wrapper = styled(FlexGroup)`
  user-select: none;
`

// Usage: Pass layout props as component props
<Wrapper align="center" justify="end">
  {children}
</Wrapper>

// ❌ BAD: Using div with hardcoded flex properties
export const Wrapper = styled.div`
  display: flex;
  align-items: center;
  justify-content: flex-end;
`

Pass Layout Props as Component Props

Don't hardcode layout properties in styled components when using layout components like FlexGroup. Pass them as props instead:

// ✅ GOOD: Pass props in JSX
export const Wrapper = styled(FlexGroup)`
  user-select: none;
`

<Wrapper align="center" justify="end">
  {children}
</Wrapper>

// ❌ BAD: Hardcoding in styled component
export const Wrapper = styled(FlexGroup)`
  align-items: center;
  justify-content: flex-end;
  user-select: none;
`

Use Gap Prop Instead of Custom Margins

Prefer `gap` prop on layout components instead of custom margins for spacing between elements:

// ✅ GOOD: Use gap prop
<Row align="center" justify="between" gap="l">
  <FlexItem>Item 1</FlexItem>
  <FlexItem>Item 2</FlexItem>
</Row>

Use Theme Spacing Instead of Magic Numbers

Always use theme spacing values instead of hardcoded pixel values:

// ✅ GOOD: Use theme spacing
export const Container = styled(Row)`
  height: ${({ theme }) => theme.core.space.space500};
  padding: 0 ${({ theme }) => theme.core.space.space200};
  margin-bottom: ${({ theme }) => theme.core.space.space200};
`;

// ❌ BAD: Using magic numbers
export const Container = styled(Row)`
  height: 64px;
  padding: 0 16px;
  margin-bottom: 16px;
`;

Use Semantic Colors from Theme

Always use semantic colors from the theme instead of CSS variables or hardcoded colors:

// ✅ GOOD: Use semantic colors
export const Header = styled(Row)`
  background-color: ${({ theme }) =>
    theme.semantic.color.background.neutral100};
  border-bottom: 1px solid
    ${({ theme }) => theme.semantic.color.border.neutral500};
`;

// ❌ BAD: Using deprecated EUI CSS variables
export const Header = styled(Row)`
  background-color: var(--euiColorEmptyShade);
  border-bottom: 1px solid var(--separatorColor);
`;

Use Layout Components (Row/Col/FlexGroup) Instead of div

Prefer layout components from the layout system instead of regular div elements:

// ✅ GOOD: Use Row component
import { Row } from 'uiSrc/components/base/layout/flex'

export const PageHeader = styled(Row)`
  height: ${({ theme }) => theme.core.space.space500};
  background-color: ${({ theme }) =>
    theme.semantic.color.background.neutral100};
`

<PageHeader align="center" justify="between" gap="l">
  {children}
</PageHeader>

// ❌ BAD: Using div with flex properties
export const PageHeader = styled.div`
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
`

Conditional Styling

Use $ prefix for transient props that shouldn't pass to DOM:

export const Button = styled.button<{ $isActive?: boolean }>`
  background-color: ${({ $isActive }) => ($isActive ? '#007bff' : '#6c757d')};
`;

Avoid !important

Never use `!important` in styled-components. Styled-components handles CSS specificity through component hierarchy. If you need to override styles, use more specific selectors or adjust the component structure:

// ✅ GOOD: Rely on CSS specificity
export const IconButton = styled(IconButton)<{ isOpen: boolean }>`
  ${({ isOpen }) =>
    isOpen &&
    css`
      background-color: ${({ theme }) =>
        theme.semantic.color.background.primary200};
    `}
`;

// ❌ BAD: Using !important
export const IconButton = styled(IconButton)`
  background-color: ${({ theme }) =>
    theme.semantic.color.background.primary200} !important;
`;

Verify Type System Compatibility

When using layout components or other typed components, verify your prop values match the type system:

// Check the component's type definitions
// FlexGroup accepts: align?: 'center' | 'stretch' | 'baseline' | 'start' | 'end'
// Use valid values from the type system

State Management (Redux)

When to Use What

• Global State (Redux):

• Data shared across multiple components
• Data persisting across routes
• Server state (API data)
• User preferences/settings

• Local State (useState):

• UI state (modals, dropdowns, tabs)
• Form inputs before submission
• Component-specific temporary data

• Derived State (Selectors):
• Computed values from Redux state
• Filtered/sorted lists
• Aggregated data

Redux Toolkit Patterns

Slice Structure

• Use createSlice from Redux Toolkit
• Define proper TypeScript types for state
• Use PayloadAction<T> for action typing
• Handle async with extraReducers and thunks

Thunks

• Use createAsyncThunk for async operations
• Handle pending, fulfilled, and rejected states
• Use rejectWithValue for error handling

Selectors

• Create basic selectors for direct state access
• Use createSelector from reselect for memoized/computed values
• Keep selectors in separate selectors.ts file

React Best Practices

Performance

• Use useCallback for functions passed as props
• Use useMemo for expensive computations
• Use React.memo for expensive components
• Avoid inline arrow functions in JSX props

Effect Cleanup

Always clean up subscriptions, timers, and event listeners in useEffect return function.

Keys in Lists

• Use unique, stable IDs (not array indices)
• Only use indices if list never reorders and items have no IDs

Conditional Rendering

• Use early returns for loading/error states
• Avoid deeply nested ternaries - extract to functions

Custom Hooks

Extract Reusable Logic

Create custom hooks for reusable stateful logic. Store component-specific hooks in the component's /hooks directory.

Form Handling

Use Formik with Yup for validation. Keep form logic in custom hooks when complex.

UI Components

⚠️ IMPORTANT:

• We are deprecating Elastic UI components
• Migrating to Redis UI (@redis-ui/*)
• Use internal wrappers from uiSrc/components/ui
• DO NOT import directly from @redis-ui/*

Component Usage

// ✅ GOOD: Import from internal wrappers
import { Button, Input, FlexGroup } from 'uiSrc/components/ui';

// ❌ BAD: Don't import directly from @redis-ui
import { Button } from '@redis-ui/components';

// ❌ DEPRECATED: Don't use Elastic UI for new code
import { EuiButton } from '@elastic/eui';

Migration Guidelines

• ✅ Use internal wrappers from uiSrc/components/ui for all new features
• ✅ Create internal wrappers for Redis UI components as needed
• ✅ Replace Elastic UI when touching existing code
• ❌ Do not import directly from @redis-ui/*
• ❌ Do not add new Elastic UI imports

Icons

⚠️ IMPORTANT: Always use icons from Redis UI library instead of custom SVGs.

Icon Usage

• Use Redis UI icons from @redis-ui/icons via iconRegistry.tsx
• Icons are automatically exported via export * from '@redis-ui/icons' in iconRegistry.tsx
• Use RiIcon component with icon type: <RiIcon type="FolderOpenIcon" />
• DO NOT create custom SVG icons - check if the icon exists in Redis UI library first

Custom Icons (Exception)

Only create custom SVG icons if:

• The icon doesn't exist in Redis UI library
• It's a project-specific icon that won't be added to the library

Testing Components

Always Use Shared renderComponent Helper

CRITICAL: Create a renderComponent helper function for each component test file:

describe('MyComponent', () => {
  const defaultProps: MyComponentProps = {
    id: faker.string.uuid(),
    name: faker.person.fullName(),
    onComplete: jest.fn(),
  }

  const renderComponent = (propsOverride?: Partial<MyComponentProps>) => {
    const props = { ...defaultProps, ...propsOverride }

    return render(
      <Provider store={store}>
        <MyComponent {...props} />
      </Provider>
    )
  }

  it('should render', () => {
    renderComponent()
    // assertions
  })
})

Benefits:

• Centralized setup and providers
• Default props in one place
• Easy prop overrides per test
• No duplicate render logic

Testing Redux

Create a test store with configureStore for components connected to Redux.

Key Principles

1. Separation of Concerns: Keep styles, types, constants, logic separate 2. Colocate Related Code: Keep sub-components and hooks close to usage 3. Consistent Naming: Follow conventions across all components 4. Type Safety: Always define proper types, never any 5. Testability: Structure for easy testing with renderComponent helper 6. Styled Components: Prefer styled-components over SCSS modules 7. Layout Components: Use FlexGroup instead of div for flex containers, pass layout props as component props 8. Type Safety: Verify prop values match component type definitions (e.g., FlexGroup's align/justify values)