State
Learn State through task board: what it does, when to use it, the code pattern, and a small task you can test immediately.
This lesson gives you
Plain meaning
State is a React pattern for one practical job. Learn the input, apply the smallest working syntax, check the output, then reuse the pattern in a real feature.
Why it matters
State matters because real React work needs consistent ways to render and update UI state. Without this pattern, the feature becomes harder to change, test and review.
Real use
In a real project, state helps build a reusable product component using tasks, filters and loading state.
Working example
Core pattern
This is the version to read first, run next, and modify last.
import { useState } from "react";
export function SaveButton() {
const [saved, setSaved] = useState(false);
return <button onClick={() => setSaved(true)}>{saved ? "Saved" : "Save"}</button>;
}Expected output
The component renders tasks, filters and loading state and updates when state or props change.
Line by line
What each part does
Line 1 sets up the State example: import { useState } from "react";.
Line 2 adds one required part of the working pattern: blank line.
Line 3 adds one required part of the working pattern: export function SaveButton() {.
Line 4 adds one required part of the working pattern: const [saved, setSaved] = useState(false);.
Line 5 exposes the output so you can verify the behavior: return <button onClick={() => setSaved(true)}>{saved ? "Saved" : "Save"}</button>;.
Line 6 adds one required part of the working pattern: }.
Methods and commands
State reference
Use these methods, commands, tags or properties with the working example above.
useState()
const [value, setValue] = useState(initial)Store local component state.
const [open, setOpen] = useState(false)
useEffect()
useEffect(() => { ... }, [deps])Run side effects after render.
useEffect(() => { loadOrders() }, [])useMemo()
useMemo(() => value, [deps])Cache expensive derived values.
const total = useMemo(() => sum(orders), [orders])
useCallback()
useCallback(() => { ... }, [deps])Keep callback identity stable.
const save = useCallback(() => submit(form), [form])
props
function Card({ title }) { ... }Pass data into components.
<StatCard label="Revenue" value={1200} />key
items.map((item) => <Row key={item.id} />)Help React track list items.
tasks.map((task) => <li key={task.id}>{task.title}</li>)controlled input
value={value} onChange={...}Keep form state in React.
<input value={email} onChange={(e) => setEmail(e.target.value)} />Try it yourself
Edit and run the concept
Change one thing at a time so the output stays easy to understand.
Terminal
SuccessReady.
Run code to see output here.
Examples
Three useful variations
Compare the examples by level. Each one keeps the same idea but changes the situation.
Beginner example
jsximport { useState } from "react";
export function SaveButton() {
const [saved, setSaved] = useState(false);
return <button onClick={() => setSaved(true)}>{saved ? "Saved" : "Save"}</button>;
}The component renders tasks, filters and loading state and updates when state or props change.
Intermediate example
jsximport { useState } from "react";
export function SaveButton() {
const [saved, setSaved] = useState(false);
return <button onClick={() => setSaved(true)}>{saved ? "Saved" : "Save"}</button>;
}The component renders tasks, filters and loading state and updates when state or props change.
Advanced example
jsximport { useState } from "react";
export function SaveButton() {
const [saved, setSaved] = useState(false);
return <button onClick={() => setSaved(true)}>{saved ? "Saved" : "Save"}</button>;
}The component renders tasks, filters and loading state and updates when state or props change.
Practice
Build understanding
Rewrite the State example for task board using your own labels or data.
Add one edge case from tasks, filters and loading state and record the output.
Explain where State fits inside a reusable product component.
Mini task
Build a tiny a reusable product component step that uses State, then write the expected output before running it.
Checklist
Use it correctly
- State is easier when connected to a real task.
- Small examples are the fastest way to catch misunderstandings.
- Practice, quiz review and projects reinforce the lesson.
- Line-by-line review turns copied code into understood code.
Common mistake
Skipping the small state example and trying to memorize the rule first.
Best practice
Use descriptive names so the example explains itself.
Interview prep
State questions
Use these as concise model answers, then rewrite them in your own words.
1. What is State in React?
State is a specific React pattern used to make a common task easier to read, write, test, or explain. A strong answer includes the purpose, a tiny example, and the result you expect after running it.
2. Why do developers use state?
State matters because real React work needs consistent ways to render and update UI state. Without this pattern, the feature becomes harder to change, test and review.
3. How would you use state in a real project?
In a real project, state helps build a reusable product component using tasks, filters and loading state. Start with the simple syntax, keep names clear, run the code, then handle one edge case before expanding the feature.
4. What mistake should a beginner avoid with state?
Skipping the small state example and trying to memorize the rule first.
5. How would you explain React Introduction in React during an interview?
React Introduction is best explained with its purpose, a small example, and one common mistake.
6. How would you explain JSX in React during an interview?
JSX is best explained with its purpose, a small example, and one common mistake.
Simple rule
Start with the working example, change one value, run it again, and explain why the output changed. That makes state useful instead of memorized.