Callback props in React Native - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to pass a callback prop named onPress to the Button component.

React Native

function MyButton({ onPress }) {
  return <Button title="Click me" [1] />;
}

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

Apress={onPress}

BonPress={onPress}

Cclick={onPress}

DonClick={onPress}

Attempts:

3 left

💡 Hint

Common Mistakes

Using onClick instead of onPress in React Native.

Forgetting to pass the callback as a prop.

In React Native, the Button component uses the onPress prop to handle press events. So you pass the callback as onPress={onPress}.

2fill in blank

medium

Complete the code to call the callback prop onPress when the button is pressed.

React Native

function MyButton({ onPress }) {
  return <Button title="Tap me" onPress={() => [1] />;
}

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

Aconsole.log('Pressed')

Balert('Pressed')

ChandlePress()

DonPress()

Attempts:

3 left

💡 Hint

Common Mistakes

Calling a different function like handlePress() that is not defined.

Logging or alerting instead of calling the callback.

To trigger the callback prop, you call it as a function inside the event handler: onPress().

3fill in blank

hard

Fix the error in the code to correctly pass a callback prop named onPress to MyButton.

React Native

function Parent() {
  function handlePress() {
    console.log('Button pressed');
  }

  return <MyButton [1] />;
}

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

AonPress={handlePress()}

BonPress="handlePress"

ConPress={handlePress}

DonPress={() => handlePress}

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the function immediately instead of passing it.

Passing the function name as a string.

You should pass the function itself as a prop, not call it immediately. So use onPress={handlePress}.

4fill in blank

hard

Fill both blanks to create a callback prop onPress that calls handlePress with argument 42.

React Native

function Parent() {
  function handlePress(value) {
    console.log(`Value is ${value}`);
  }

  return <MyButton onPress={() => [1]([2])} />;
}

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

AhandlePress

B42

ChandlePress()

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Putting parentheses in the first blank like handlePress().

Using a variable name instead of the actual argument.

You pass an arrow function that calls handlePress with the argument 42 when pressed.

5fill in blank

hard

Fill all three blanks to define a MyButton component that accepts an onPress callback prop and calls it when pressed.

React Native

function MyButton({ [1] }) {
  return <Button title="Press me" [2]={() => [3]()} />;
}

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

AonPress

DhandlePress

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the prop and the event handler.

Not calling the function inside the arrow function.

The component receives the onPress prop and calls onPress() when the button is pressed.

Practice

1. What is the main purpose of using callback props in React Native components?

easy

A. To manage component state internally

B. To style components dynamically

C. To allow child components to communicate events back to parent components

D. To fetch data from an API

Solution

1. Step 1: Understand callback props role

   Callback props are functions passed from parent to child to notify the parent about events.

2. Step 2: Identify communication direction

   They let children send information or events back to parents, enabling communication.

3. Final Answer:

   To allow child components to communicate events back to parent components -> Option C

4. Quick Check:

   Callback props = child-to-parent communication [OK]

Hint: Callback props let children tell parents about events [OK]

Common Mistakes:

• Thinking callback props manage styling
• Confusing callback props with state management
• Assuming callback props fetch data

2. Which of the following is the correct way to pass a callback prop named onPress from a parent to a child component in React Native?

easy

A.

B.

C. handlePress />

D.

Solution

1. Step 1: Recall JSX prop syntax

   Props are passed as attributes with values inside curly braces for functions.

2. Step 2: Match correct syntax

   uses onPress={handlePress}, which is valid JSX syntax.

3. Final Answer:

   <ChildComponent onPress={handlePress} /> -> Option A

4. Quick Check:

   JSX props use = and curly braces for functions [OK]

Hint: Use = and curly braces to pass functions as props [OK]

Common Mistakes:

• Using colon : instead of =
• Using arrow => inside prop
• Adding parentheses () in prop name

3. Given the code below, what will be logged when the button is pressed?

function Parent() {
  const handleClick = () => console.log('Clicked!');
  return <Child onPress={handleClick} />;
}

function Child({ onPress }) {
  return <Button title="Press me" onPress={onPress} />;
}

medium

A. Nothing happens

B. Clicked!

C. Error: onPress is not a function

D. Button title is logged

Solution

1. Step 1: Trace callback prop usage

   The Parent passes handleClick as onPress prop to Child.

2. Step 2: Check Child button onPress

   The Child uses onPress prop as the button's onPress handler, so pressing calls handleClick.

3. Final Answer:

   Clicked! -> Option B

4. Quick Check:

   Button press triggers parent's callback [OK]

Hint: Child calls parent's function on event [OK]

Common Mistakes:

• Assuming onPress is undefined
• Thinking button title logs
• Ignoring callback function call

4. Identify the error in this React Native code snippet:

function Parent() {
  const handlePress = () => alert('Pressed');
  return <Child onPress={handlePress()} />;
}

function Child({ onPress }) {
  return <Button title="Click" onPress={onPress} />;
}

medium

A. alert cannot be used in React Native

B. Child component is missing props destructuring

C. Button component does not support onPress

D. handlePress is called immediately instead of passed as a function

Solution

1. Step 1: Analyze prop passing

   In onPress={handlePress()}, the function is called immediately, passing its result (undefined) instead of the function.

2. Step 2: Understand correct usage

   We should pass the function itself without calling it: onPress={handlePress}.

3. Final Answer:

   handlePress is called immediately instead of passed as a function -> Option D

4. Quick Check:

   Pass function reference, not call it [OK]

Hint: Pass function, don't call it when passing as prop [OK]

Common Mistakes:

• Calling function instead of passing reference
• Thinking alert is invalid in React Native
• Ignoring destructuring in Child

5. You want a child component to notify the parent when a text input changes, but only if the input length is more than 3 characters. How should you implement the callback prop pattern to achieve this?

hard

A. Pass a callback prop from parent; child calls it only when input length > 3

B. Child manages input state and updates parent state directly

C. Parent listens to child's internal state without callback

D. Use a global variable to share input value between components

Solution

1. Step 1: Understand callback prop usage for conditional events

   The parent passes a function as a prop to the child to receive input changes.

2. Step 2: Implement conditional call in child

   The child calls the callback only if the input length is more than 3, controlling when to notify the parent.

3. Final Answer:

   Pass a callback prop from parent; child calls it only when input length > 3 -> Option A

4. Quick Check:

   Child controls event call; parent receives updates [OK]

Hint: Child calls parent callback only when condition meets [OK]

Common Mistakes:

• Letting child update parent state directly
• Ignoring conditional logic in child
• Using global variables for communication