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)

Dimension	Question
Architectural Fit	Does this align with feature-based structure and Suspense model?
Complexity Load	How complex is state, data, and interaction logic?
Performance Risk	Does it introduce rendering, bundle, or CLS risk?
Reusability	Can this be reused without modification?
Maintenance Cost	How hard will this be to reason about in 6 months?

Score Formula

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

Range: -5 → +15

Interpretation

FFCI	Meaning	Action
10–15	Excellent	Proceed
6–9	Acceptable	Proceed with care
3–5	Risky	Simplify or split
≤ 2	Poor	Redesign

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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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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

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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

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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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5. Import Aliases (Required)

Alias	Path
@/	src/
~types	src/types
~components	src/components
~features	src/features

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

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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>.

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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.

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10. Loading & Error Handling

Absolute Rule

❌ Never return early loaders
✅ Always rely on Suspense boundaries

User Feedback

• useMuiSnackbar only
• No third-party toast libraries

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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.

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12. TypeScript Standards

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

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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;

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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

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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

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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

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18. Skill Status

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