Mengelola Keadaan Komponen dengan useState
Perkenalkan hook useState, simpan nilai penghitung atau sakelar dalam keadaan, lalu picu perenderan ulang dengan memanggil fungsi pengatur keadaan.
Mengelola Keadaan Komponen dengan useState adalah pelajaran React Native Academy gratis di CoddyKit. Ini adalah pelajaran 2 dari 4. Kamu bisa membaca pelajaran lengkapnya di bawah secara gratis — lalu praktikkan langsung di browser dengan editor kode bawaan dan tutor AI 24/7. Ini adalah bagian dari jalur belajar React Native Academy, dan progresmu tersinkronisasi di web dan aplikasi CoddyKit. Kursus React Native Academy mencakup 4 pelajaran total.
Bagian dari pelajaran ini belum diterjemahkan dan ditampilkan dalam bahasa Inggris.
What Is State?
State is data that can change over time and that a component owns and manages internally. Unlike props (which come from the parent and are read-only), state is created and updated by the component itself. When state changes, React automatically re-renders the component to reflect the new values in the UI. Common state examples include: whether a modal is open, the text the user has typed, the currently selected tab, or items fetched from an API. State is what makes React components interactive.
import { View, Text, TouchableOpacity } from 'react-native';
import { useState } from 'react';
export default function Counter() {
// Declare state: count starts at 0
const [count, setCount] = useState(0);
return (
<View style={{ padding: 24, alignItems: 'center' }}>
<Text style={{ fontSize: 48, fontWeight: 'bold' }}>{count}</Text>
<TouchableOpacity
onPress={() => setCount(count + 1)}
style={{ marginTop: 16, padding: 12, backgroundColor: '#4f86f7', borderRadius: 8 }}
>
<Text style={{ color: '#fff', fontSize: 18 }}>Increment</Text>
</TouchableOpacity>
</View>
);
}The useState Hook Signature
useState is a React Hook that you call at the top level of your component function. It takes one argument — the initial state value — and returns an array with two elements: the current state value and a setter function. You destructure these using array destructuring. The naming convention is [value, setValue]. The setter function is what you call to update state — never mutate the state variable directly. Each state variable is independent; call useState multiple times for multiple pieces of state.
import { useState } from 'react';
function MyComponent() {
// Syntax: const [value, setter] = useState(initialValue);
const [count, setCount] = useState(0); // number
const [name, setName] = useState(''); // string
const [isVisible, setIsVisible] = useState(false); // boolean
const [items, setItems] = useState([]); // array
const [user, setUser] = useState(null); // object or null
// Update state by calling the setter:
// setCount(5); ← sets to 5
// setName('Alice'); ← sets to 'Alice'
// setIsVisible(true); ← sets to true
}State Updates Trigger Re-Renders
When you call a state setter, React schedules a re-render of the component. During the next render, useState returns the new value. React is smart about this — it batches multiple state updates that happen in the same event handler and does a single re-render. Also important: the state value inside the current render is immutable. Calling setCount(count + 1) does not immediately change count in the current function execution — the new value appears in the next render cycle.
import { useState } from 'react';
import { View, Text, TouchableOpacity } from 'react-native';
export default function Example() {
const [count, setCount] = useState(0);
function handlePress() {
// These do NOT stack: count is still 0 in this render
setCount(count + 1); // schedules count = 1
setCount(count + 1); // also schedules count = 1, not 2!
// To correctly base on previous value, use functional update:
// setCount(prev => prev + 1); // prev = 0, result = 1
// setCount(prev => prev + 1); // prev = 1, result = 2
}
return (
<TouchableOpacity onPress={handlePress}>
<Text>{count}</Text>
</TouchableOpacity>
);
}Functional Updates with Previous State
When your new state depends on the previous state, always use the functional update form: setState(prev => prev + 1). React guarantees that prev is the most recent state value, even if multiple updates are batched. This is critical when incrementing counters, toggling booleans, or adding items to arrays in rapid succession (e.g., fast button taps). The object literal form (setState(state + 1)) can produce bugs when multiple updates happen before the component re-renders.
import { useState } from 'react';
import { View, Text, TouchableOpacity } from 'react-native';
export default function SafeCounter() {
const [count, setCount] = useState(0);
function increment() {
// Safe: uses previous state, handles batching correctly
setCount(prev => prev + 1);
}
function decrement() {
setCount(prev => Math.max(0, prev - 1)); // min 0
}
function reset() {
setCount(0); // direct value ok when not based on previous
}
return (
<View style={{ alignItems: 'center', gap: 12, padding: 24 }}>
<Text style={{ fontSize: 48 }}>{count}</Text>
<TouchableOpacity onPress={increment}><Text>+</Text></TouchableOpacity>
<TouchableOpacity onPress={decrement}><Text>-</Text></TouchableOpacity>
<TouchableOpacity onPress={reset}><Text>Reset</Text></TouchableOpacity>
</View>
);
}Toggling Boolean State
A very common pattern is toggling a boolean state between true and false. Use the functional update form with the logical NOT operator: setIsOpen(prev => !prev). This is cleaner than setIsOpen(!isOpen) because it correctly handles rapid presses. Common use cases include showing/hiding a modal, expanding/collapsing an accordion section, switching between play and pause, or toggling a favorite star icon. Booleans are perhaps the most frequently used type of component state.
import { useState } from 'react';
import { View, Text, TouchableOpacity, Modal, StyleSheet } from 'react-native';
export default function ToggleModal() {
const [isVisible, setIsVisible] = useState(false);
return (
<View style={styles.container}>
<TouchableOpacity
style={styles.btn}
onPress={() => setIsVisible(prev => !prev)}
>
<Text style={styles.btnText}>Toggle Modal</Text>
</TouchableOpacity>
<Modal visible={isVisible} transparent animationType='fade'>
<View style={styles.overlay}>
<Text style={styles.modalText}>Hello from the modal!</Text>
<TouchableOpacity onPress={() => setIsVisible(false)}>
<Text style={{ color: '#fff', marginTop: 16 }}>Close</Text>
</TouchableOpacity>
</View>
</Modal>
</View>
);
}
const styles = StyleSheet.create({
container: { flex: 1, justifyContent: 'center', alignItems: 'center' },
btn: { padding: 12, backgroundColor: '#4f86f7', borderRadius: 8 },
btnText: { color: '#fff', fontWeight: 'bold' },
overlay: { flex: 1, backgroundColor: 'rgba(0,0,0,0.7)', justifyContent: 'center', alignItems: 'center' },
modalText: { color: '#fff', fontSize: 20, fontWeight: 'bold' },
});State with Strings: Controlled Text Input
Binding a TextInput to state creates a controlled input. The value prop sets the displayed text (from state), and the onChangeText callback updates the state whenever the user types. This makes the state the single source of truth for the input's value — you can read, validate, or transform the text at any time by reading the state variable. Without binding to state (uncontrolled), you would need a ref to read the input value, which is less idiomatic in React.
import { useState } from 'react';
import { View, Text, TextInput, StyleSheet } from 'react-native';
export default function SearchBox() {
const [query, setQuery] = useState('');
return (
<View style={styles.container}>
<TextInput
value={query}
onChangeText={setQuery} // same as: (text) => setQuery(text)
placeholder='Search...'
style={styles.input}
/>
<Text style={styles.preview}>
You typed: <Text style={{ fontWeight: 'bold' }}>{query}</Text>
</Text>
<Text style={styles.count}>{query.length} characters</Text>
</View>
);
}
const styles = StyleSheet.create({
container: { padding: 16, gap: 8 },
input: { borderWidth: 1, borderColor: '#ccc', borderRadius: 8, padding: 12, fontSize: 16 },
preview: { fontSize: 14, color: '#555' },
count: { fontSize: 12, color: '#999' },
});State with Arrays: Adding and Removing Items
When state is an array, never mutate it directly with push or splice. Instead, create a new array with the change and pass it to the setter. To add an item: setItems(prev => [...prev, newItem]). To remove an item: setItems(prev => prev.filter(item => item.id !== id)). To update an item: setItems(prev => prev.map(item => item.id === id ? {...item, done: true} : item)). These immutable patterns let React detect changes and schedule efficient re-renders.
import { useState } from 'react';
import { View, Text, TouchableOpacity, TextInput, FlatList } from 'react-native';
export default function TodoList() {
const [todos, setTodos] = useState([]);
const [input, setInput] = useState('');
function addTodo() {
if (!input.trim()) return;
setTodos(prev => [...prev, { id: Date.now().toString(), text: input.trim(), done: false }]);
setInput('');
}
function toggleDone(id) {
setTodos(prev => prev.map(t => t.id === id ? { ...t, done: !t.done } : t));
}
return (
<View style={{ flex: 1, padding: 16 }}>
<TextInput value={input} onChangeText={setInput} placeholder='Add a todo' />
<TouchableOpacity onPress={addTodo}><Text>Add</Text></TouchableOpacity>
<FlatList
data={todos}
keyExtractor={t => t.id}
renderItem={({ item }) => (
<TouchableOpacity onPress={() => toggleDone(item.id)}>
<Text style={{ textDecorationLine: item.done ? 'line-through' : 'none' }}>
{item.text}
</Text>
</TouchableOpacity>
)}
/>
</View>
);
}State with Objects
For related pieces of state, group them into a single object state variable. When updating object state, spread the previous state to keep unchanged fields: setState(prev => ({ ...prev, name: 'Alice' })). This only overwrites the name field while keeping all other fields intact. Alternatively, each field can be its own useState — neither approach is universally better. Use an object when the fields always change together (like a form with name, email, and password); use separate states when they change independently.
import { useState } from 'react';
import { View, TextInput, Text, StyleSheet } from 'react-native';
export default function ProfileForm() {
const [form, setForm] = useState({
name: '',
email: '',
bio: '',
});
function updateField(field, value) {
setForm(prev => ({ ...prev, [field]: value }));
}
return (
<View style={{ padding: 16, gap: 12 }}>
<TextInput
value={form.name}
onChangeText={v => updateField('name', v)}
placeholder='Name'
style={styles.input}
/>
<TextInput
value={form.email}
onChangeText={v => updateField('email', v)}
placeholder='Email'
style={styles.input}
/>
<Text style={{ color: '#666' }}>Preview: {form.name} — {form.email}</Text>
</View>
);
}
const styles = StyleSheet.create({
input: { borderWidth: 1, borderColor: '#ccc', borderRadius: 8, padding: 12 },
});Lazy Initial State
If computing the initial state is expensive (reading from AsyncStorage, parsing a large dataset), pass a function to useState instead of a value: useState(() => computeExpensiveValue()). React calls this initializer function only once on the component's first render, not on every subsequent render. This is called lazy initialization. Passing an expensive computation as a plain value (useState(expensiveCompute())) would run it on every render, causing unnecessary work even though the initial state is only used once.
import { useState } from 'react';
// Without lazy init: computeExpensiveList() runs on EVERY render
const [list, setList] = useState(computeExpensiveList()); // BAD
// With lazy init: function is called ONCE on mount
const [list, setList] = useState(() => computeExpensiveList()); // GOOD
// Real example: JSON.parse is cheap, but still good practice:
const [settings, setSettings] = useState(() => {
const stored = SomeStorage.get('settings');
return stored ? JSON.parse(stored) : { theme: 'light', lang: 'en' };
});Derived Values vs. Redundant State
Don't store values in state if they can be derived from existing state or props. For example, if you have a list of todos in state, don't also store a completedCount in state — compute it as todos.filter(t => t.done).length during render. Storing derived values in state creates synchronization bugs: you forget to update one when you update the other. Only put things in state that you can't derive, can't compute during render, or that are asynchronously set (like API response data). This rule keeps state minimal and bug-free.
import { useState } from 'react';
import { Text, View } from 'react-native';
export default function TodoStats() {
const [todos, setTodos] = useState([
{ id: '1', text: 'Buy groceries', done: true },
{ id: '2', text: 'Write code', done: false },
{ id: '3', text: 'Go for a walk', done: true },
]);
// DERIVED: computed from existing state, not stored in state
const total = todos.length;
const completed = todos.filter(t => t.done).length;
const remaining = total - completed;
return (
<View style={{ padding: 16 }}>
<Text>Total: {total}</Text>
<Text>Completed: {completed}</Text>
<Text>Remaining: {remaining}</Text>
</View>
);
}useState vs useRef: When Not to Use State
Not every value that changes in a component needs to be in state. If a value changes but does not need to trigger a re-render, store it in a useRef instead. Common examples: a timer ID returned from setTimeout, a flag tracking whether a network request is in flight, or the previous value of a prop. Putting these in state causes unnecessary re-renders. A useRef persists its value across renders (like state) but updating it does not schedule a re-render. The golden rule: if the UI doesn't need to change when the value changes, use useRef.
import { useState, useRef, useEffect } from 'react';
import { Text, TouchableOpacity, View } from 'react-native';
export default function Timer() {
const [elapsed, setElapsed] = useState(0);
const intervalRef = useRef(null); // timer ID in ref — no re-render needed
function start() {
if (intervalRef.current) return; // already running
intervalRef.current = setInterval(() => {
setElapsed(prev => prev + 1); // state — needs re-render to show
}, 1000);
}
function stop() {
clearInterval(intervalRef.current);
intervalRef.current = null;
}
useEffect(() => () => clearInterval(intervalRef.current), []); // cleanup
return (
<View style={{ alignItems: 'center', padding: 24, gap: 16 }}>
<Text style={{ fontSize: 48 }}>{elapsed}s</Text>
<TouchableOpacity onPress={start}><Text>Start</Text></TouchableOpacity>
<TouchableOpacity onPress={stop}><Text>Stop</Text></TouchableOpacity>
</View>
);
}Quick Check
Test your understanding of React Native Mobile Development concepts from this lesson.
Lesson Recap
In this lesson you learned: useState declares state variables and provides a setter that triggers re-renders, functional updates safely derive new state from the previous value, and derived values should be computed during render instead of stored as redundant state. Next up we explore lifting state up to share data between sibling components.
Belajar JavaScript dengan tutor AI — gratis
Tulis dan jalankan kode asli di browser kamu, dapatkan bantuan instan dari tutor AI 24/7, dan lanjutkan di mana kamu tinggalkan di web atau aplikasi.
- Kursus
- 30
- Pelajaran
- 120
Pertanyaan yang Sering Diajukan
Apakah pelajaran “Mengelola Keadaan Komponen dengan useState” gratis?
Ya — teks lengkap “Mengelola Keadaan Komponen dengan useState” gratis dibaca di sini di web. Untuk praktiknya secara interaktif (editor kode bawaan dan tutor AI 24/7) dan buka sisa kursus React Native Academy, upgrade ke CoddyKit PRO. Kursus React Native Academy mencakup 4 pelajaran total.
Apa yang akan aku pelajari di “Mengelola Keadaan Komponen dengan useState”?
Perkenalkan hook useState, simpan nilai penghitung atau sakelar dalam keadaan, lalu picu perenderan ulang dengan memanggil fungsi pengatur keadaan. Kamu berlatih React Native Academy dengan kode praktik yang langsung kamu jalankan di browser, dan tutor AI 24/7 menjawab pertanyaanmu saat kamu mengerjakan pelajaran ini.
Apakah aku perlu pengalaman untuk memulai React Native Academy?
Tidak diperlukan pengalaman sebelumnya. React Native Academy di CoddyKit dirancang untuk pemula hingga pelajar tingkat lanjut, jadi kamu bisa memulai di sini atau dari awal dan belajar sesuai kecepatan kamu sendiri. Ini adalah pelajaran 2 dari 4.
Berapa lama pelajaran “Mengelola Keadaan Komponen dengan useState” memakan waktu?
Sebagian besar pelajaran CoddyKit memakan waktu sekitar 5–10 menit. Setiap pelajaran ringkas dan interaktif, jadi kamu membuat kemajuan stabil dan melanjutkan dari tempat kamu tinggalkan di web dan aplikasi.
Bisakah aku menulis dan menjalankan kode dalam pelajaran React Native Academy ini?
Ya. Setiap pelajaran React Native Academy menyertakan editor kode bawaan, jadi kamu menulis dan menjalankan kode nyata langsung di browser dan mendapatkan umpan balik AI instan — tidak diperlukan penyiapan lokal.
Semua pelajaran dalam kursus ini
- Mengirim Data dengan Props
- Mengelola Keadaan Komponen dengan useState
- Mengangkat Keadaan ke Atas
- Membangun Aplikasi Penghitung Interaktif