State and hooks in client components in NextJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the React hook needed to manage state in a client component.

NextJS

import React, { [1] } from 'react';

Drag options to blanks, or click blank then click option'

AuseState

BuseContext

CuseEffect

DuseRef

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a hook that manages side effects instead of state.

Confusing useState with useEffect or useRef.

The useState hook is used to add state to functional components in React and Next.js client components.

2fill in blank

medium

Complete the code to declare a state variable called 'count' with initial value 0.

NextJS

const [count, [1]] = useState(0);

Drag options to blanks, or click blank then click option'

AsetCount

BchangeCount

CupdateCount

DcountSetter

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different function name that is not linked to the state variable.

Confusing the state variable name with the updater function.

The second element returned by useState is the function used to update the state variable. By convention, it is named starting with 'set' followed by the state variable name.

3fill in blank

hard

Complete the button text by adding a descriptive label before the count value.

NextJS

"use client";

import { useState } from 'react';

export default function Counter() {
  const [count, setCount] = useState(0);
  return <button onClick={() => setCount(count + 1)}>[1]{count}</button>;
}

Drag options to blanks, or click blank then click option'

AClick me:

BCount:

CPress:

DValue:

Attempts:

3 left

💡 Hint

Common Mistakes

Using unclear or unrelated labels.

Omitting the label which can confuse users.

The string before the count value in the button helps users understand what the number means. 'Count: ' is a clear label.

4fill in blank

hard

Fill in the blank to create a button that increments the count state by 1 when clicked.

NextJS

const [count, setCount] = useState(0);

return <button onClick={() => setCount(count [1] 1)}>Increment</button>;

Drag options to blanks, or click blank then click option'

A/

B-

C+

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

Confusing the order of operators.

The increment operation adds 1 to the current count using the + operator: setCount(count + 1).

5fill in blank

hard

Fill all three blanks to create a stateful input component that updates its value on change.

NextJS

const [value, [1]] = useState('');

return <input type="text" value={value} onChange={e => [2]([3])} />;

Drag options to blanks, or click blank then click option'

AsetValue

Be.target.value

Cvalue

DsetCount

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong updater function name.

Passing the wrong value to the updater function.

Confusing the state variable with the updater function.

The state updater function setValue is called with the new input value e.target.value when the input changes. The current state variable value is used as the input's value.

Practice

1. What is the main purpose of using useState in a Next.js client component?

easy

A. To fetch data from the server before rendering

B. To store and update data that changes over time within the component

C. To style the component dynamically

D. To navigate between pages automatically

Solution

1. Step 1: Understand what useState does

   useState is a React hook that allows components to keep track of data that can change, like user input or toggles.

2. Step 2: Identify the purpose in Next.js client components

   In Next.js client components, useState helps remember and update values without reloading the page.

3. Final Answer:

   To store and update data that changes over time within the component -> Option B

4. Quick Check:

   State = Remember and update data [OK]

Hint: Remember: useState stores changing data inside components [OK]

Common Mistakes:

• Thinking useState fetches server data
• Confusing useState with styling or navigation
• Forgetting useState only works in client components

2. Which of the following is the correct way to declare a state variable called count with initial value 0 in a Next.js client component?

easy

A. const [count, setCount] = useState(0);

B. const count = useState(0);

C. let count = useState(0);

D. const count = useState()[0];

Solution

1. Step 1: Recall the syntax of useState hook

   The correct syntax uses array destructuring: const [state, setState] = useState(initialValue);

2. Step 2: Match the syntax with the variable name and initial value

   For count starting at 0, it should be const [count, setCount] = useState(0);

3. Final Answer:

   const [count, setCount] = useState(0); -> Option A

4. Quick Check:

   useState syntax = [state, setState] [OK]

Hint: Use array destructuring: [value, setValue] = useState() [OK]

Common Mistakes:

• Assigning useState directly to a single variable
• Using let instead of const for state
• Not using array destructuring syntax

3. Consider this Next.js client component code:

"use client";
import { useState } from 'react';

export default function Counter() {
  const [count, setCount] = useState(0);
  return (
     setCount(count + 1)}>
      Count: {count}
    
  );
}

What will be displayed after clicking the button three times?

medium

A. Count: 0

B. Count: 1

C. Count: 3

D. Count: undefined

Solution

1. Step 1: Understand initial state and button click effect

   The initial count is 0. Each click calls setCount(count + 1), increasing count by 1.

2. Step 2: Calculate count after three clicks

   After 1 click: count = 1
   After 2 clicks: count = 2
   After 3 clicks: count = 3

3. Final Answer:

   Count: 3 -> Option C

4. Quick Check:

   Increment count 3 times = 3 [OK]

Hint: Each click adds 1 to count state [OK]

Common Mistakes:

• Thinking count resets on each render
• Confusing initial value with updated value
• Ignoring that setCount updates state asynchronously

4. What is wrong with this Next.js client component code?

import { useState } from 'react';

export default function Toggle() {
  const [isOn, setIsOn] = useState(false);
  return (
     setIsOn(!isOn)}>
      {isOn ? 'ON' : 'OFF'}
    
  );
}

medium

A. State variable should be declared with let

B. Incorrect use of useState syntax

C. Button onClick handler is invalid

D. Missing 'use client'; directive at the top

Solution

1. Step 1: Check for client component requirement

   Hooks like useState require the component to be a client component, which needs 'use client'; at the top.

2. Step 2: Verify code for missing directive

   The code lacks 'use client'; at the top, so it will cause an error in Next.js.

3. Final Answer:

   Missing 'use client'; directive at the top -> Option D

4. Quick Check:

   Client components need 'use client' [OK]

Hint: Always add 'use client'; on top when using hooks [OK]

Common Mistakes:

• Forgetting 'use client' directive
• Thinking useState syntax is wrong
• Assuming onClick handler is invalid

5. You want to create a Next.js client component that toggles between showing and hiding a message when a button is clicked. Which code snippet correctly implements this behavior?

hard

A. "use client";
import { useState } from 'react';

export default function ShowHide() {
const [visible, setVisible] = useState(false);
return (
<>
setVisible(!visible)}>
{visible ? 'Hide' : 'Show'} Message

{visible && Hello, this is the message!}
</>
);
}

B. "use client";
import { useState } from 'react';

export default function ShowHide() {
const visible = false;
return (
<>
(visible = !visible)}>
{visible ? 'Hide' : 'Show'} Message

{visible && Hello, this is the message!}
</>
);
}

C. import { useState } from 'react';

export default function ShowHide() {
const [visible, setVisible] = useState(false);
return (
<>
setVisible(!visible)}>
{visible ? 'Hide' : 'Show'} Message

{visible && Hello, this is the message!}
</>
);
}

D. "use client";
import { useState } from 'react';

export default function ShowHide() {
const [visible, setVisible] = useState(false);
return (
<>
setVisible(visible)}>
{visible ? 'Hide' : 'Show'} Message

{visible && Hello, this is the message!}
</>
);
}

Solution

1. Step 1: Check for 'use client' directive and useState usage

   "use client"; import { useState } from 'react'; export default function ShowHide() { const [visible, setVisible] = useState(false); return ( <> setVisible(!visible)}> {visible ? 'Hide' : 'Show'} Message {visible &&

   Hello, this is the message!

   } </> ); } correctly includes 'use client'; and uses useState to track visibility state.

2. Step 2: Verify toggle logic and rendering

   The button toggles visible state with setVisible(!visible), and the message shows only when visible is true.

3. Final Answer:

   Option A code snippet correctly implements the toggle behavior -> Option A

4. Quick Check:

   Toggle state with useState and 'use client' [OK]

Hint: Use useState and 'use client'; toggle with setVisible(!visible) [OK]

Common Mistakes:

• Not adding 'use client' directive
• Trying to change state variable directly
• Passing current state to setter without toggling