tomevault-io React Hooks Best Practices Skill
This skill covers React Hooks patterns, custom hooks, and dependency management.
When to Use
Use this skill when:
- Writing custom hooks
- Managing component state
- Handling side effects
- Optimizing with memoization
Core Principle
EXTRACT AND REUSE - Extract reusable logic into custom hooks. Keep components focused on rendering.
Custom Hook Patterns
Basic Custom Hook
import { useState, useCallback } from 'react';
interface UseToggleReturn {
value: boolean;
toggle: () => void;
setTrue: () => void;
setFalse: () => void;
}
export function useToggle(initialValue = false): UseToggleReturn {
const [value, setValue] = useState(initialValue);
const toggle = useCallback(() => setValue((v) => !v), []);
const setTrue = useCallback(() => setValue(true), []);
const setFalse = useCallback(() => setValue(false), []);
return { value, toggle, setTrue, setFalse };
}
Data Fetching Hook
import { useState, useEffect } from 'react';
interface UseQueryResult<T> {
data: T | null;
error: Error | null;
isLoading: boolean;
refetch: () => void;
}
export function useQuery<T>(
queryFn: () => Promise<T>,
deps: unknown[] = []
): UseQueryResult<T> {
const [data, setData] = useState<T | null>(null);
const [error, setError] = useState<Error | null>(null);
const [isLoading, setIsLoading] = useState(true);
const fetchData = useCallback(async () => {
setIsLoading(true);
setError(null);
try {
const result = await queryFn();
setData(result);
} catch (err) {
setError(err instanceof Error ? err : new Error('Unknown error'));
} finally {
setIsLoading(false);
}
}, deps);
useEffect(() => {
fetchData();
}, [fetchData]);
return { data, error, isLoading, refetch: fetchData };
}
Form Hook
import { useState, useCallback, ChangeEvent, FormEvent } from 'react';
interface UseFormReturn<T> {
values: T;
errors: Partial<Record<keyof T, string>>;
handleChange: (e: ChangeEvent<HTMLInputElement>) => void;
handleSubmit: (onSubmit: (values: T) => void) => (e: FormEvent) => void;
reset: () => void;
setFieldValue: (field: keyof T, value: T[keyof T]) => void;
}
export function useForm<T extends Record<string, unknown>>(
initialValues: T
): UseFormReturn<T> {
const [values, setValues] = useState<T>(initialValues);
const [errors, setErrors] = useState<Partial<Record<keyof T, string>>>({});
const handleChange = useCallback((e: ChangeEvent<HTMLInputElement>) => {
const { name, value, type, checked } = e.target;
setValues((prev) => ({
...prev,
[name]: type === 'checkbox' ? checked : value,
}));
}, []);
const handleSubmit = useCallback(
(onSubmit: (values: T) => void) => (e: FormEvent) => {
e.preventDefault();
onSubmit(values);
},
[values]
);
const reset = useCallback(() => {
setValues(initialValues);
setErrors({});
}, [initialValues]);
const setFieldValue = useCallback((field: keyof T, value: T[keyof T]) => {
setValues((prev) => ({ ...prev, [field]: value }));
}, []);
return { values, errors, handleChange, handleSubmit, reset, setFieldValue };
}
Dependency Array Management
Correct Dependencies
// ✅ All dependencies included
useEffect(() => {
fetchUser(userId);
}, [userId]);
// ✅ Stable callback with useCallback
const handleClick = useCallback(() => {
onClick(id);
}, [onClick, id]);
useEffect(() => {
document.addEventListener('click', handleClick);
return () => document.removeEventListener('click', handleClick);
}, [handleClick]);
Common Mistakes
// ❌ Missing dependency
useEffect(() => {
fetchUser(userId); // userId not in deps
}, []);
// ❌ Object/array causing infinite loops
useEffect(() => {
doSomething(options); // options is new object each render
}, [options]);
// ✅ Fix: Use useMemo or extract values
const { page, limit } = options;
useEffect(() => {
doSomething({ page, limit });
}, [page, limit]);
Stable References
// ❌ Function recreated each render
function Component({ onSave }: { onSave: (data: Data) => void }): React.ReactElement {
useEffect(() => {
const handler = () => onSave(data);
window.addEventListener('beforeunload', handler);
return () => window.removeEventListener('beforeunload', handler);
}, [onSave, data]); // onSave might change
}
// ✅ Use useCallback in parent or useRef
function Component({ onSave }: { onSave: (data: Data) => void }): React.ReactElement {
const
onSaveRef.current = onSave;
useEffect(() => {
const handler = () => onSaveRef.current(data);
window.addEventListener('beforeunload', handler);
return () => window.removeEventListener('beforeunload', handler);
}, [data]); // Stable reference
}
Effect Cleanup
Subscription Cleanup
useEffect(() => {
const subscription = eventEmitter.subscribe(handleEvent);
return () => {
subscription.unsubscribe();
};
}, [handleEvent]);
Abort Controller for Fetch
useEffect(() => {
const controller = new AbortController();
async function fetchData(): Promise<void> {
try {
const response = await fetch(url, { signal: controller.signal });
const data = await response.json();
setData(data);
} catch (err) {
if (err instanceof Error && err.name !== 'AbortError') {
setError(err);
}
}
}
fetchData();
return () => controller.abort();
}, [url]);
Timer Cleanup
useEffect(() => {
const timerId = setInterval(() => {
setCount((c) => c + 1);
}, 1000);
return () => clearInterval(timerId);
}, []);
Memoization Patterns
useMemo for Expensive Computations
const sortedItems = useMemo(() => {
return items.slice().sort((a, b) => a.name.localeCompare(b.name));
}, [items]);
const filteredData = useMemo(() => {
return data.filter((item) => item.status === filter);
}, [data, filter]);
useCallback for Stable Functions
// ✅ Stable function for child components
const handleSelect = useCallback((id: string) => {
setSelectedId(id);
onSelect?.(id);
}, [onSelect]);
// ✅ Stable function for effects
const fetchData = useCallback(async () => {
const result = await api.getData(params);
setData(result);
}, [params]);
When NOT to Memoize
// ❌ Premature optimization
const name = useMemo(() => `${firstName} ${lastName}`, [firstName, lastName]);
// ✅ Simple computation - no memoization needed
const name = `${firstName} ${lastName}`;
// ❌ Memoizing primitives
const isActive = useMemo(() => status === 'active', [status]);
// ✅ Direct comparison
const isActive = status === 'active';
Hook Rules
- Only call at top level - Not in loops, conditions, or nested functions
- Only call in React functions - Components or custom hooks
- Start with 'use' - Custom hook naming convention
- Keep hooks pure - Same inputs = same outputs
// ❌ Conditional hook call
function Component({ shouldFetch }: { shouldFetch: boolean }): React.ReactElement {
if (shouldFetch) {
const data = useQuery(fetchData); // Error!
}
}
// ✅ Always call, conditionally use
function Component({ shouldFetch }: { shouldFetch: boolean }): React.ReactElement {
const data = useQuery(fetchData, { enabled: shouldFetch });
}
Testing Custom Hooks
import { renderHook, act } from '@testing-library/react';
import { useToggle } from '../useToggle';
describe('useToggle', () => {
it('initializes with false by default', () => {
const { result } = renderHook(() => useToggle());
expect(result.current.value).toBe(false);
});
it('toggles value', () => {
const { result } = renderHook(() => useToggle());
act(() => {
result.current.toggle();
});
expect(result.current.value).toBe(true);
});
});
Best Practices Summary
- Extract reusable logic - Create custom hooks
- Include all dependencies - Let ESLint guide you
- Use stable references - useCallback, useMemo, useRef
- Clean up effects - Return cleanup function
- Avoid premature memoization - Profile first
- Name with 'use' prefix - Convention for custom hooks
- Keep hooks focused - Single responsibility
Notes
- Use TanStack Query for data fetching (better than custom hooks)
- Use Zustand/Jotai for global state (instead of Context + hooks)
- Consider React 19's use() hook for promises and context
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