Default props in React Native - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a default value for the title prop in a React Native component.

React Native

function Header({ title = [1] }) {
  return <Text>{title}</Text>;
}

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

Aundefined

Bnull

C"Welcome"

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using null or undefined as default will render nothing.

Forgetting to use quotes around string default values.

Setting a default value for the title prop ensures the component shows "Welcome" if no title is passed.

2fill in blank

medium

Complete the code to assign default props using the defaultProps property.

React Native

const Button = ({ label }) => <Text>{label}</Text>;

Button.[1] = {
  label: [2]
};

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

AdefaultProps

BpropsDefault

C"Click me"

D"Press"

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect property names like propsDefault.

Not quoting string default values.

The defaultProps property sets default values for props. Here, label defaults to "Click me".

3fill in blank

hard

Fix the error in the code to properly set default props for a functional component.

React Native

function Label(props) {
  return <Text>{props.text}</Text>;
}

Label.defaultProps = [1];

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

A{ text: 'Default Text' }

B[ text: 'Default Text' ]

C"Default Text"

Dtext = 'Default Text'

Attempts:

3 left

💡 Hint

Common Mistakes

Using array syntax instead of object.

Assigning a string directly instead of an object.

Default props must be an object with keys matching prop names and their default values.

4fill in blank

hard

Fill both blanks to set default props and use them in the component.

React Native

const Greeting = ({ name = [1] }) => {
  return <Text>Hello, [2]!</Text>;
};

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

A"Guest"

Bname

Cuser

D"User"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string literal instead of the prop variable inside JSX.

Not setting a default value for the prop.

The default value for name is "Guest". The component uses the name prop inside the text.

5fill in blank

hard

Fill all three blanks to define default props and use them in a React Native component.

React Native

function Info({ title = [1], subtitle = [2] }) {
  return (
    <View>
      <Text>{ [3] }</Text>
      <Text>{subtitle}</Text>
    </View>
  );
}

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

A"No Title"

B"No Subtitle"

Ctitle

D"Title"

Attempts:

3 left

💡 Hint

Common Mistakes

Using string literals instead of prop variables inside JSX.

Not setting default values for both props.

Default props title and subtitle are set to strings. The component displays title and subtitle correctly.

Practice

1. What is the main purpose of default props in a React Native component?

easy

A. To provide fallback values when no props are passed

B. To force the user to always pass props

C. To style the component automatically

D. To make the component stateful

Solution

1. Step 1: Understand what happens when props are missing

   If a prop is not passed, the component might break or behave unexpectedly.

2. Step 2: Role of default props

   Default props provide a fallback value so the component still works smoothly without explicit props.

3. Final Answer:

   To provide fallback values when no props are passed -> Option A

4. Quick Check:

   Default props = fallback values [OK]

Hint: Default props fill missing values automatically [OK]

Common Mistakes:

• Thinking default props force prop passing
• Confusing default props with styling
• Assuming default props make components stateful

2. Which of the following is the correct way to set a default prop value in a React Native functional component?

easy

A. MyComponent.propTypes = { title: 'Hello' }

B. function MyComponent(props = { title: 'Hello' }) { ... }

C. function MyComponent({ title = 'Hello' }) { ... }

D. const MyComponent = (props) => { props.title = 'Hello' }

Solution

1. Step 1: Identify default prop syntax in function parameters

   Using destructuring with default values like { title = 'Hello' } is the modern and correct way.

2. Step 2: Check other options

   function MyComponent(props = { title: 'Hello' }) { ... } wrongly assigns default to whole props object, C uses propTypes which is for validation not defaults, D mutates props which is bad practice.

3. Final Answer:

   function MyComponent({ title = 'Hello' }) { ... } -> Option C

4. Quick Check:

   Destructure with default = correct syntax [OK]

Hint: Use destructuring with = for default props [OK]

Common Mistakes:

• Assigning default to entire props object
• Confusing propTypes with defaultProps
• Mutating props inside component

3. What will be displayed by this component if used as <Greeting /> without passing any props?

function Greeting({ name = 'Guest' }) {
  return Hello, {name}!;
}

medium

A. Hello, !

B. Hello, Guest!

C. Hello, undefined!

D. Error: name is required

Solution

1. Step 1: Check default prop value

   The parameter name has a default value 'Guest' if no prop is passed.

2. Step 2: Analyze component output

   Since no name prop is passed, it uses 'Guest' and renders 'Hello, Guest!'.

3. Final Answer:

   Hello, Guest! -> Option B

4. Quick Check:

   Default prop used = 'Guest' [OK]

Hint: Default prop shows when no prop passed [OK]

Common Mistakes:

• Expecting empty or undefined name
• Thinking component throws error without prop
• Ignoring default parameter syntax

4. Identify the error in this component that tries to set default props:

function Button(props) {
  return {props.label};
}

Button.defaultProps = {
  label: 'Click me'
};

medium

A. defaultProps is not supported on functional components

B. defaultProps should be set inside the function parameters

C. The component should use destructuring for props

D. There is no error; this is correct

Solution

1. Step 1: Check if defaultProps works on functional components

   React Native supports defaultProps on functional components, so this is valid.

2. Step 2: Verify syntax correctness

   The syntax used is correct and will provide default label if none passed.

3. Final Answer:

   There is no error; this is correct -> Option D

4. Quick Check:

   defaultProps on function = valid [OK]

Hint: defaultProps works on functions too [OK]

Common Mistakes:

• Assuming defaultProps only works on classes
• Thinking destructuring is mandatory
• Confusing defaultProps with state

5. You want a component to show a default color 'blue' but only if the passed color prop is a non-empty string. Which is the best way to set this default in a React Native functional component?

hard

A. function Box({ color }) { color = color ? color : 'blue'; ... }

B. function Box({ color = 'blue' }) { ... }

C. function Box({ color }) { color &&= 'blue'; ... }

D. function Box({ color = '' }) { if (color) color = 'blue'; ... }

Solution

1. Step 1: Understand default parameter limits

   Default parameters only apply if the prop is undefined, not empty string.

2. Step 2: Choose a method that checks for non-empty string

   Using a conditional (color ? color : 'blue') ensures empty strings get replaced by 'blue'.

3. Step 3: Compare options

   A fails if color is empty string (uses empty). C's color &&= 'blue' sets 'blue' only if color is truthy (opposite). D's if (color) sets 'blue' only if truthy (wrong).

4. Final Answer:

   function Box({ color }) { color = color ? color : 'blue'; ... } -> Option A

5. Quick Check:

   Conditional check handles empty string default [OK]

Hint: Use conditional to handle empty strings as default [OK]

Common Mistakes:

• Relying only on default parameters for empty strings
• Using &&= which sets value when truthy
• Using if (color) which triggers on truthy