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Escrevendo hooks personalizados

Extraia a lógica com estado para um hook personalizado reutilizável, compartilhe-o entre dois componentes e siga a convenção de nomenclatura e as regras dos hooks.

Escrevendo hooks personalizados é uma aula grátis de React Native Academy no CoddyKit. Esta é a aula 4 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de React Native Academy, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de React Native Academy inclui 4 aulas no total.

Partes desta aula ainda não foram traduzidas e aparecem em inglês.

What Are Custom Hooks?

Custom hooks are JavaScript functions whose names start with use and that may call other React hooks inside them. They let you extract stateful logic from a component into a reusable function. The logic is shared, but each component that calls the custom hook gets its own isolated state — custom hooks are not singletons.

The Rules of Hooks Apply to Custom Hooks

Custom hooks follow the same rules as built-in hooks: only call hooks at the top level (not inside loops or conditions), and only call hooks from React function components or other custom hooks. The use naming prefix is required — it signals to React and linters that the function follows these rules.

// Valid custom hook — starts with 'use'
function useCounter(initialValue) {
  const [count, setCount] = useState(initialValue);
  const increment = () => setCount(c => c + 1);
  const decrement = () => setCount(c => c - 1);
  const reset = () => setCount(initialValue);
  return { count, increment, decrement, reset };
}

A useCounter Custom Hook

The useCounter hook encapsulates a counter's state and its increment, decrement, and reset actions. Any component that needs a counter can call useCounter without repeating the state management logic. Each call to the hook creates an independent counter.

function CounterScreen() {
  const { count, increment, decrement, reset } = useCounter(0);

  return (
    <View>
      <Text>Count: {count}</Text>
      <Button title='+' onPress={increment} />
      <Button title='-' onPress={decrement} />
      <Button title='Reset' onPress={reset} />
    </View>
  );
}

A useFetch Custom Hook

A useFetch hook wraps the common pattern of fetching data with useEffect: it manages loading, data, and error states internally, and exposes them to the component. The URL is a dependency — changing it re-triggers the fetch.

function useFetch(url) {
  const [data, setData] = useState(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);

  useEffect(() => {
    setLoading(true);
    fetch(url)
      .then((res) => res.json())
      .then((json) => { setData(json); setLoading(false); })
      .catch((err) => { setError(err); setLoading(false); });
  }, [url]);

  return { data, loading, error };
}

Using the useFetch Hook

Components using useFetch become dramatically simpler. The component only describes what to render for each state (loading, error, data) without managing any fetch logic itself. If the same endpoint is needed in another screen, just call useFetch again — no code duplication.

function PostsScreen() {
  const { data, loading, error } = useFetch('https://jsonplaceholder.typicode.com/posts');

  if (loading) return <ActivityIndicator />;
  if (error) return <Text>Error: {error.message}</Text>;

  return (
    <FlatList
      data={data}
      keyExtractor={(item) => String(item.id)}
      renderItem={({ item }) => <Text>{item.title}</Text>}
    />
  );
}

A useToggle Custom Hook

A useToggle hook simplifies managing boolean state that needs to switch between true and false. It is useful for modals, accordions, dark mode, or any feature that toggles. The hook returns the current value and a stable toggle function.

function useToggle(initialValue = false) {
  const [value, setValue] = useState(initialValue);
  const toggle = useCallback(() => setValue((v) => !v), []);
  return [value, toggle];
}

// Usage
const [isVisible, toggleVisible] = useToggle(false);
<Button title='Show/Hide' onPress={toggleVisible} />
<Modal visible={isVisible} ... />

A useForm Custom Hook

A useForm hook manages a form's field values, change handler, and reset action. This pattern eliminates boilerplate in forms across the app. The hook accepts an object of initial field values and returns the current values, a generic field change handler, and a reset function.

function useForm(initialValues) {
  const [values, setValues] = useState(initialValues);

  const handleChange = useCallback((field, value) => {
    setValues((prev) => ({ ...prev, [field]: value }));
  }, []);

  const reset = useCallback(() => setValues(initialValues), [initialValues]);

  return { values, handleChange, reset };
}

A useNetworkStatus Custom Hook

A useNetworkStatus hook wraps the NetInfo API to expose the device's online/offline status. Components can simply read the boolean value without knowing about event subscription setup and teardown — the hook handles that internally with a useEffect cleanup function.

import NetInfo from '@react-native-community/netinfo';

function useNetworkStatus() {
  const [isOnline, setIsOnline] = useState(true);

  useEffect(() => {
    const unsubscribe = NetInfo.addEventListener((state) => {
      setIsOnline(state.isConnected ?? true);
    });
    return unsubscribe; // cleanup on unmount
  }, []);

  return isOnline;
}

Sharing Logic Between Components

The real power of custom hooks is sharing logic, not UI. Two screens can both call useNetworkStatus and each gets its own subscription. If the hook has a side effect (like a subscription), it is automatically cleaned up when the component using it unmounts. Each component's hook instance is fully independent.

// Both screens share the same logic, not the same state
function HomeScreen() {
  const isOnline = useNetworkStatus();
  return <Text>{isOnline ? 'Online' : 'Offline'}</Text>;
}

function ProfileScreen() {
  const isOnline = useNetworkStatus(); // independent subscription
  return <Banner visible={!isOnline} message='No connection' />;
}

Custom Hook Naming and Organization

Name custom hooks descriptively: useAuth, useCart, useDebounce, useWindowDimensions. Store hooks in a dedicated hooks/ directory to keep them organized and findable. Each hook should have a single clear responsibility — avoid creating hooks that do five unrelated things.

// Project structure
src/
  hooks/
    useAuth.js
    useFetch.js
    useForm.js
    useToggle.js
    useNetworkStatus.js

A useDebounce Custom Hook

A useDebounce hook delays propagating a value until a specified time has passed since the last update. This is perfect for search inputs where you want to wait until the user stops typing before firing an API request. The hook uses useEffect and a timer to manage the delay.

function useDebounce(value, delay) {
  const [debouncedValue, setDebouncedValue] = useState(value);

  useEffect(() => {
    const timer = setTimeout(() => {
      setDebouncedValue(value);
    }, delay);
    return () => clearTimeout(timer);
  }, [value, delay]);

  return debouncedValue;
}

// Usage
const debouncedQuery = useDebounce(searchQuery, 400);
useEffect(() => { fetchResults(debouncedQuery); }, [debouncedQuery]);

Quick Check

Test your understanding of writing custom hooks from this lesson.

Lesson Recap

In this lesson you learned: custom hooks are functions starting with 'use' that encapsulate stateful logic, each component calling a custom hook gets its own independent state and effects, and organize hooks in a dedicated hooks/ directory for a single responsibility per hook. Next up we explore the Context API for sharing global state without prop drilling.

Perguntas Frequentes

A aula “Escrevendo hooks personalizados” é grátis?

Sim — o texto completo de “Escrevendo hooks personalizados” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de React Native Academy, atualize para CoddyKit PRO. O curso de React Native Academy inclui 4 aulas no total.

O que vou aprender em “Escrevendo hooks personalizados”?

Extraia a lógica com estado para um hook personalizado reutilizável, compartilhe-o entre dois componentes e siga a convenção de nomenclatura e as regras dos hooks. Você pratica React Native Academy com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.

Preciso ter experiência prévia para começar React Native Academy?

Nenhuma experiência prévia é necessária. React Native Academy no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 4 de 4.

Quanto tempo leva a aula “Escrevendo hooks personalizados”?

A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.

Posso escrever e executar código nesta aula de React Native Academy?

Sim. Cada aula de React Native Academy inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.

Todas as aulas deste curso

useRef para nós do DOM e valores mutáveis
useReducer para lógica de estado complexa
useCallback e useMemo para desempenho
Escrevendo hooks personalizados

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