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.

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

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

3. When to Use This Skill

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

4. 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

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/

5. Import Aliases (Required)

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

6. 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>.

7. 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

8. 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' }),
});

9. 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.

10. Loading & Error Handling

Absolute Rule

❌ Never return early loaders ✅ Always rely on Suspense boundaries

User Feedback

• •useMuiSnackbar only
• •No third-party toast libraries

11. Performance Defaults

• •useMemo for expensive derivations
• •useCallback for passed handlers
• •React.memo for heavy pure components
• •Debounce search (300–500ms)
• •Cleanup effects to avoid leaks

Performance regressions are bugs.

12. TypeScript Standards

• •Strict mode enabled
• •No implicit any
• •Explicit return types
• •JSDoc on public interfaces
• •Types colocated with feature

13. Canonical File Structure

src/
  features/
    my-feature/
      api/
      components/
      hooks/
      helpers/
      types/
      index.ts

  components/
    SuspenseLoader/
    CustomAppBar/

  routes/
    my-route/
      index.tsx

14. Canonical Component Template

import React, { useState, useCallback } from 'react';
import { Box, Paper } from '@mui/material';
import { useSuspenseQuery } from '@tanstack/react-query';
import { featureApi } from '../api/featureApi';
import type { FeatureData } from '~types/feature';

interface MyComponentProps {
  id: number;
  onAction?: () => void;
}

export const MyComponent: React.FC<MyComponentProps> = ({ id, onAction }) => {
  const [state, setState] = useState('');

  const { data } = useSuspenseQuery<FeatureData>({
    queryKey: ['feature', id],
    queryFn: () => featureApi.getFeature(id),
  });

  const handleAction = useCallback(() => {
    setState('updated');
    onAction?.();
  }, [onAction]);

  return (
    <Box sx={{ p: 2 }}>
      <Paper sx={{ p: 3 }}>
        {/* Content */}
      </Paper>
    </Box>
  );
};

export default MyComponent;

15. Anti-Patterns (Immediate Rejection)

❌ Early loading returns ❌ Feature logic in components/ ❌ Shared state via prop drilling instead of hooks ❌ Inline API calls ❌ Untyped responses ❌ Multiple responsibilities in one component

16. Integration With Other Skills

• •frontend-design → Visual systems & aesthetics
• •page-cro → Layout hierarchy & conversion logic
• •analytics-tracking → Event instrumentation
• •backend-dev-guidelines → API contract alignment
• •error-tracking → Runtime observability

17. Operator Validation Checklist

Before finalizing code:

• • FFCI ≥ 6
• • Suspense used correctly
• • Feature boundaries respected
• • No early returns
• • Types explicit and correct
• • Lazy loading applied
• • Performance safe

18. Skill Status

Status: Stable, opinionated, and enforceable Intended Use: Production React codebases with long-term maintenance horizons

When to Use

This skill is applicable to execute the workflow or actions described in the overview.