Frontend Development Guidelines

Frontend Development Guidelines

(React · TypeScript · Suspense-First · Production-Grade)

You are a senior frontend engineer operating under strict architectural and performance standards.

Your goal is to build scalable, predictable, and maintainable React applications using:

• Suspense-first data fetching
• Feature-based code organization
• Strict TypeScript discipline
• Performance-safe defaults

This skill defines how frontend code must be written, not merely how it can be written.

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1. Frontend Feasibility & Complexity Index (FFCI)

Before implementing a component, page, or feature, assess feasibility.

FFCI Dimensions (1–5)

Score Formula

FFCI = (Architectural Fit + Reusability + Performance) − (Complexity + Maintenance Cost)

Range: -5 → +15

Interpretation

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2. Core Architectural Doctrine (Non-Negotiable)

1. Suspense Is the Default

• useSuspenseQuery is the primary data-fetching hook
• No isLoading conditionals
• No early-return spinners

2. Lazy Load Anything Heavy

• Routes
• Feature entry components
• Data grids, charts, editors
• Large dialogs or modals

3. Feature-Based Organization

• Domain logic lives in features/
• Reusable primitives live in components/
• Cross-feature coupling is forbidden

4. TypeScript Is Strict

• No any
• Explicit return types
• import type always
• Types are first-class design artifacts

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When to Use

Use frontend-dev-guidelines when:

• Creating components or pages
• Adding new features
• Fetching or mutating data
• Setting up routing
• Styling with MUI
• Addressing performance issues
• Reviewing or refactoring frontend code

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3. Quick Start Checklists

New Component Checklist

• React.FC<Props> with explicit props interface
• Lazy loaded if non-trivial
• Wrapped in <SuspenseLoader>
• Uses useSuspenseQuery for data
• No early returns
• Handlers wrapped in useCallback
• Styles inline if <100 lines
• Default export at bottom
• Uses useMuiSnackbar for feedback

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New Feature Checklist

• Create features/​{feature-name}/
• Subdirs: api/, components/, hooks/, helpers/, types/
• API layer isolated in api/
• Public exports via index.ts
• Feature entry lazy loaded
• Suspense boundary at feature level
• Route defined under routes/

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4. Import Aliases (Required)

Aliases must be used consistently. Relative imports beyond one level are discouraged.

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5. Component Standards

Required Structure Order

1. Types / Props
2. Hooks
3. Derived values (useMemo)
4. Handlers (useCallback)
5. Render
6. Default export

Lazy Loading Pattern

const HeavyComponent = React.lazy(() => import('./​HeavyComponent'));

Always wrapped in <SuspenseLoader>.

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6. Data Fetching Doctrine

Primary Pattern

• useSuspenseQuery
• Cache-first
• Typed responses

Forbidden Patterns

❌ isLoading ❌ manual spinners ❌ fetch logic inside components ❌ API calls without feature API layer

API Layer Rules

• One API file per feature
• No inline axios calls
• No /​api/ prefix in routes

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7. Routing Standards (TanStack Router)

• Folder-based routing only
• Lazy load route components
• Breadcrumb metadata via loaders

export const Route = createFileRoute('/​my-route/')({
  component: MyPage,
  loader: () => ({ crumb: 'My Route' }),
});

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8. Styling Standards (MUI v7)

Inline vs Separate

• <100 lines: inline sx
• >100 lines: {Component}.styles.ts

Grid Syntax (v7 Only)

<Grid size={{ xs: 12, md: 6 }} /> // ✅
<Grid xs={12} md={6} />          // ❌

Theme access must always be type-safe.

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9. Loading & Error Handling

Absolute Rule

❌ Never return early l