What are props in React - Quick Revision & Key Takeaways

Recall & Review

beginner

What are props in React?

Props are inputs to React components. They are like function arguments that let you pass data from a parent component to a child component.

beginner

How do you pass props to a React component?

You pass props by adding attributes to the component tag, like <MyComponent name="Alice" />. The child component receives them as an object.

beginner

Can props be changed inside a React component?

No, props are read-only. A component should never modify its own props. To change data, use state or pass new props from the parent.

beginner

Why are props important in React?

Props let components be reusable and dynamic by receiving different data. They help build a clear data flow from parent to child components.

beginner

Example: How to access a prop named 'title' inside a functional component?

Inside the function, use props.title or use object destructuring like function MyComponent({ title }) { ... } to access the title prop.

What does 'props' stand for in React?

A Properties passed to components

B Private variables inside components

C Functions to update state

D CSS styles for components

Props are short for properties and are used to pass data to components.

Can a React component modify its own props?

A No, props are read-only

B Only if using useState

C Yes, anytime

D Only in class components

Props are read-only and should never be changed inside the component.

How do you pass a prop named 'color' with value 'blue' to a component?

A <Component color: 'blue' />

B <Component color={blue} />

C <Component color='blue' />

D <Component 'color'='blue' />

Props are passed as attributes with values in quotes or curly braces for expressions.

Inside a functional component, how do you access props?

A Using context API only

B Using this.props

C Using state variable

D Using props parameter or destructuring

Functional components receive props as a parameter, which can be used directly or destructured.

Why are props useful in React?

A To style components

B To pass data and make components reusable

C To store local state

D To handle events only

Props allow components to receive data and be reused with different inputs.

Explain what props are in React and how they help components communicate.

Think about how you give instructions or data to a friend.

Describe how to pass and access props in a functional React component with an example.

Imagine sending a letter with a name on it and reading it inside.

Practice

1. What are props in React?

easy

A. Data passed from a parent component to a child component

B. A way to store component state internally

C. Functions that update the component's state

D. A method to style components

Solution

1. Step 1: Understand the role of props

   Props are used to send data from a parent component down to a child component in React.

2. Step 2: Differentiate props from state and methods

   Props are not for storing state or styling; they are inputs like function arguments.

3. Final Answer:

   Data passed from a parent component to a child component -> Option A

4. Quick Check:

   Props = Parent to child data [OK]

Hint: Props are like function arguments passed down [OK]

Common Mistakes:

• Confusing props with state
• Thinking props change inside the child
• Believing props are used for styling

2. Which of the following is the correct way to pass a prop named title with value "Hello" to a component Greeting?

easy

A.

B.

C.

D.

Solution

1. Step 1: Recognize JSX prop syntax

   Props are passed as attributes with key-value pairs inside JSX tags, using quotes for strings.

2. Step 2: Check each option's syntax

   correctly uses title="Hello". misses the key, C uses unquoted value, D misses quotes.

3. Final Answer:

   <Greeting title="Hello" /> -> Option D

4. Quick Check:

   Props syntax = key="value" [OK]

Hint: Props look like HTML attributes with quotes [OK]

Common Mistakes:

• Omitting the prop name
• Not quoting string values
• Using curly braces without variables

3. Given this component:

function Welcome(props) {
  return <h1>Hello, {props.name}!</h1>;
}

// Usage:
<Welcome name="Alice" />

What will be rendered on the screen?

medium

A. Hello, props.name!

B. Hello, !

C. Hello, Alice!

D. Error: props is undefined

Solution

1. Step 1: Identify how props are used in the component

   The component uses props.name inside JSX to display the passed name.

2. Step 2: Check the usage of the component

   The component is called with name="Alice", so props.name equals "Alice".

3. Final Answer:

   Hello, Alice! -> Option C

4. Quick Check:

   props.name = Alice [OK]

Hint: Props values appear where you use {props.key} [OK]

Common Mistakes:

• Printing the literal string 'props.name'
• Forgetting to pass the prop
• Assuming props is undefined

4. What is wrong with this React component usage?

function Message(props) {
  return <p>{props.text}</p>;
}

// Usage:
<Message text=Hello />

medium

A. The function should return a string, not JSX

B. The prop value Hello should be in quotes

C. Props cannot be used inside <p> tags

D. The component name should be lowercase

Solution

1. Step 1: Check the prop syntax in usage

   The prop text=Hello is missing quotes around the string value.

2. Step 2: Recall JSX rules for string props

   String props must be quoted like text="Hello" or wrapped in curly braces if a variable.

3. Final Answer:

   The prop value Hello should be in quotes -> Option B

4. Quick Check:

   String props need quotes [OK]

Hint: Always quote string props in JSX [OK]

Common Mistakes:

• Leaving string props unquoted
• Using lowercase component names
• Misunderstanding JSX return types

5. You want to create a reusable Button component that shows different labels based on props. Which approach correctly uses props to achieve this?

function Button(props) {
  return <button>{props.label}</button>;
}

// Usage:
<Button label="Save" />
<Button label="Cancel" />

hard

A. This approach works because props.label changes the button text dynamically

B. This approach is wrong because props cannot be used inside button tags

C. You must use state instead of props to change button labels

D. Button labels must be hardcoded inside the component

Solution

1. Step 1: Understand props usage for dynamic content

   Props allow passing different values to the same component to show varied content.

2. Step 2: Verify the example usage

   The Button component uses props.label inside the button, and different labels are passed in usage.

3. Final Answer:

   This approach works because props.label changes the button text dynamically -> Option A

4. Quick Check:

   Props enable reusable components [OK]

Hint: Use props to customize component content easily [OK]

Common Mistakes:

• Thinking props can't change displayed text
• Confusing props with state for static labels
• Hardcoding values inside components