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React with TypeScript Quiz

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Question 1/15

How can you extend interfaces in TypeScript when creating a React component?

interface BaseProps {
    id: string;
}

interface AdvancedProps extends BaseProps {
    date: Date;
}

const Component: React.FC<AdvancedProps> = ({ id, date }) => (
    <div>{id}: {date.toISOString()}</div>
);

Select your answer

By using `implements` keyword.

By creating a utility type.

By using the `extends` keyword.

By merging objects in the component.

Question 2/15

How do you define a prop that accepts children in TypeScript with React?

interface MyComponentProps {
    children?: React.ReactNode;
}

const MyComponent: React.FC<MyComponentProps> = ({ children }) => {
    return <div>{children}</div>;
};

Select your answer

By defining the prop type as `React.ReactNode`.

By defining the prop type as `Element`.

By defining the prop type as `JSX.Element`.

By defining the prop type as `ReactElement`.

Question 3/15

How does TypeScript handle missing props when destructuring in a function component?

interface MyComponentProps {
    name: string;
    age?: number;
}

const MyComponent: React.FC<MyComponentProps> = ({ name, age = 0 }) => (
    <div>{name}, {age}</div>
);

Select your answer

By setting all destructured values to `null`.

By ignoring missing values without warning.

By setting default values during destructuring or marking props as optional.

By throwing a compile-time error.

Question 4/15

What is the `key` prop used for in React lists?

const items = ['a', 'b', 'c'];

const listItems = items.map((item, index) => (
    <li key={index}>{item}</li>
));

Select your answer

To create a reference pointer for each element.

To set a unique id for each HTML element.

To disable an item in a list.

To help React identify which items have changed in a list for efficient re-rendering.

Question 5/15

How do you type a component that takes a prop function with a return type of `Promise` using TypeScript with React?

interface AsyncComponentProps {
    fetchData: () => Promise<void>;
}

const AsyncComponent: React.FC<AsyncComponentProps> = ({ fetchData }) => {
    useEffect(() => {
        fetchData();
    }, [fetchData]);
    return <div>Data has been fetched.</div>;
};

Select your answer

Declaring the function inside `useEffect`.

Using `async` in the function signature inside the component.

Defining a prop with a function type that returns `Promise`.

Annotating the component as `React.AsyncComponent`.

Question 6/15

How can you define and use a custom hook with TypeScript in a React component?

function useCustomHook() {
    const [value, setValue] = useState<string>("");
    return { value, setValue };
}

const MyComponent: React.FC = () => {
    const { value, setValue } = useCustomHook();
    return <input value={value} onChange={e => setValue(e.target.value)} />;
};

Select your answer

Create it as a standalone JavaScript function without types.

Declare it as a class method for managing state.

Define the hook as a regular function using TypeScript types and use it inside the component.

Use `React.useHook` to define the hook and call it in the component.

Question 7/15

In a TypeScript React component, how can you specify that a prop is optional?

interface MyComponentProps {
    name?: string;
}

const MyComponent: React.FC<MyComponentProps> = ({ name }) => {
    return <div>{name}</div>;
};

Select your answer

By initializing the prop with `null`.

By using `?` after the prop name.

By using `undefined` in the prop type.

By using an `Optional` type alias.

Question 8/15

Which hook is used to set up initial state in a TypeScript functional component?

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

Select your answer

useState

useEffect

useContext

useReducer

Question 9/15

How can you ensure a component in TypeScript only accepts props of a specific shape using TypeScript?

interface ButtonProps {
    label: string;
    onClick: () => void;
}

const Button: React.FC<ButtonProps> = ({ label, onClick }) => (
    <button onClick={onClick}>{label}</button>
);

Select your answer

Use `PropTypes` like in JavaScript React.

Directly declare types in the function body after JSX.

Use dynamic prop types with the `any` type.

Use an interface to define the prop types and use it in the component type definition.

Question 10/15

How do you enforce that a certain number of times a component rerenders when a particular prop changes in TypeScript?

class MyComponent extends React.Component<{ inputValue: number }> {
    componentDidUpdate(prevProps: { inputValue: number }) {
        if (prevProps.inputValue !== this.props.inputValue) {
            console.log('Rerendered!');
        }
    }
}

Select your answer

Using state variables to count rerenders manually within the component.

You don't directly enforce rerender times; React manages rendering based on prop or state changes.

By writing a custom `shouldComponentUpdate` method that increments each time.

By editing React's internal render processes (not recommended).

Question 11/15

Given the following TypeScript code, what type does the `setColor` function accept?

const [color, setColor] = useState<string | null>(null);

Select your answer

Either a string or null.

Only null values.

Only numbers.

Only strings.

Question 12/15

When using a `useReducer` hook in TypeScript, what type parameters should be provided?

type State = {count: number};
type Action = {type: 'increment'} | {type: 'decrement'};

const reducer = (state: State, action: Action): State => {
    switch (action.type) {
        case 'increment':
            return {count: state.count + 1};
        case 'decrement':
            return {count: state.count - 1};
        default:
            return state;
    }
};

Select your answer

Only the state type, as action can be inferred.

The state and action types for the reducer function.

Only the action type, as state is self-inferable.

Component props and reducer return type.

Question 13/15

In TypeScript, how do you prevent assigning `undefined` to a prop?

interface MyComponentProps {
    name: string;
}

const MyComponent: React.FC<MyComponentProps> = ({ name }) => {
    return <div>Hello, {name}</div>;
};

Select your answer

With default parameters in the function implementation.

By initializing the prop with an empty string.

By using `undefined` in the type restriction.

By not using the `?` modifier in the interface declaration.

Question 14/15

What is the purpose of the `React.FC` type in a TypeScript React component?

const MyComponent: React.FC = () => {
    return <div>Hello, World!</div>;
};

Select your answer

To declare state in a functional component.

To define a class component.

To handle side effects in a component.

To type the props of a functional component.

Question 15/15

In TypeScript, what is a Discriminated Union and how is it useful in React?

type LoadingState = {
    state: 'loading';
};

type SuccessState = {
    state: 'success';
    response: string;
};

type ErrorState = {
    state: 'error';
    error: Error;
};

interface StateContainer {
    stateObject: LoadingState | SuccessState | ErrorState;
}

const Component: React.FC<StateContainer> = ({ stateObject }) => {
    switch (stateObject.state) {
        case 'loading':
            return <div>Loading...</div>;
        case 'success':
            return <div>{stateObject.response}</div>;
        case 'error':
            return <div>Error: {stateObject.error.message}</div>;
        default:
            return null;
    }
};

Select your answer

A type that ignores type safety for the sake of flexibility.

A type that allows multiple inheritance in TypeScript.

An alias for a generic type.

A type that combines multiple types with shared identifiers to allow narrowed type checking based on specific values.

Your Results

You did not answer any questions correctly.

Your Answers

Question 1/15

😊 Your answer was correct 🙁 Your answer was incorrect

How can you extend interfaces in TypeScript when creating a React component?

interface BaseProps {
    id: string;
}

interface AdvancedProps extends BaseProps {
    date: Date;
}

const Component: React.FC<AdvancedProps> = ({ id, date }) => (
    <div>{id}: {date.toISOString()}</div>
);

Available answers

By using `implements` keyword.

By creating a utility type.

By using the `extends` keyword.

By merging objects in the component.

In TypeScript, interfaces can be extended using the

extends

keyword, which allows one interface to inherit and augment another.

Question 2/15

😊 Your answer was correct 🙁 Your answer was incorrect

How do you define a prop that accepts children in TypeScript with React?

interface MyComponentProps {
    children?: React.ReactNode;
}

const MyComponent: React.FC<MyComponentProps> = ({ children }) => {
    return <div>{children}</div>;
};

Available answers

By defining the prop type as `React.ReactNode`.

By defining the prop type as `Element`.

By defining the prop type as `JSX.Element`.

By defining the prop type as `ReactElement`.

In React with TypeScript, the

React.ReactNode

type is used to type the

children

prop, as it represents anything that can be rendered in a React component.

Question 3/15

😊 Your answer was correct 🙁 Your answer was incorrect

How does TypeScript handle missing props when destructuring in a function component?

interface MyComponentProps {
    name: string;
    age?: number;
}

const MyComponent: React.FC<MyComponentProps> = ({ name, age = 0 }) => (
    <div>{name}, {age}</div>
);

Available answers

By setting all destructured values to `null`.

By ignoring missing values without warning.

By setting default values during destructuring or marking props as optional.

By throwing a compile-time error.

TypeScript will require a default value in the destructuring if a prop marked as optional is missing, avoiding runtime errors by setting a default value.

Question 4/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is the `key` prop used for in React lists?

const items = ['a', 'b', 'c'];

const listItems = items.map((item, index) => (
    <li key={index}>{item}</li>
));

Available answers

To create a reference pointer for each element.

To set a unique id for each HTML element.

To disable an item in a list.

To help React identify which items have changed in a list for efficient re-rendering.

The

key

prop is crucial for React's list rendering because it helps React identify which items have changed, added, or removed, improving the efficiency of the re-rendering process.

Question 5/15

😊 Your answer was correct 🙁 Your answer was incorrect

How do you type a component that takes a prop function with a return type of `Promise<void>` using TypeScript with React?

interface AsyncComponentProps {
    fetchData: () => Promise<void>;
}

const AsyncComponent: React.FC<AsyncComponentProps> = ({ fetchData }) => {
    useEffect(() => {
        fetchData();
    }, [fetchData]);
    return <div>Data has been fetched.</div>;
};

Available answers

Declaring the function inside `useEffect`.

Using `async` in the function signature inside the component.

Defining a prop with a function type that returns `Promise<void>`.

Annotating the component as `React.AsyncComponent`.

In this context, the prop is typed using a specific function signature

() => Promise<void>

to indicate it returns a promise resolving void.

Question 6/15

😊 Your answer was correct 🙁 Your answer was incorrect

How can you define and use a custom hook with TypeScript in a React component?

function useCustomHook() {
    const [value, setValue] = useState<string>("");
    return { value, setValue };
}

const MyComponent: React.FC = () => {
    const { value, setValue } = useCustomHook();
    return <input value={value} onChange={e => setValue(e.target.value)} />;
};

Available answers

Create it as a standalone JavaScript function without types.

Declare it as a class method for managing state.

Define the hook as a regular function using TypeScript types and use it inside the component.

Use `React.useHook` to define the hook and call it in the component.

A custom hook in TypeScript is defined as a regular function that may use other hooks internally, and you specify the types as needed.

Question 7/15

😊 Your answer was correct 🙁 Your answer was incorrect

In a TypeScript React component, how can you specify that a prop is optional?

interface MyComponentProps {
    name?: string;
}

const MyComponent: React.FC<MyComponentProps> = ({ name }) => {
    return <div>{name}</div>;
};

Available answers

By initializing the prop with `null`.

By using `?` after the prop name.

By using `undefined` in the prop type.

By using an `Optional` type alias.

In TypeScript, you can make a prop optional by adding

after the prop name in the interface.

Question 8/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which hook is used to set up initial state in a TypeScript functional component?

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

Available answers

useState

useEffect

useContext

useReducer

The

useState

hook is used to set up local state in a functional component. You can specify the type using generics, such as

useState<number>

Question 9/15

😊 Your answer was correct 🙁 Your answer was incorrect

How can you ensure a component in TypeScript only accepts props of a specific shape using TypeScript?

interface ButtonProps {
    label: string;
    onClick: () => void;
}

const Button: React.FC<ButtonProps> = ({ label, onClick }) => (
    <button onClick={onClick}>{label}</button>
);

Available answers

Use `PropTypes` like in JavaScript React.

Directly declare types in the function body after JSX.

Use dynamic prop types with the `any` type.

Use an interface to define the prop types and use it in the component type definition.

In TypeScript, interfaces or types are used to explicitly define the shape of props a component accepts, ensuring type safety and auto-completion.

Question 10/15

😊 Your answer was correct 🙁 Your answer was incorrect

How do you enforce that a certain number of times a component rerenders when a particular prop changes in TypeScript?

class MyComponent extends React.Component<{ inputValue: number }> {
    componentDidUpdate(prevProps: { inputValue: number }) {
        if (prevProps.inputValue !== this.props.inputValue) {
            console.log('Rerendered!');
        }
    }
}

Available answers

Using state variables to count rerenders manually within the component.

You don't directly enforce rerender times; React manages rendering based on prop or state changes.

By writing a custom `shouldComponentUpdate` method that increments each time.

By editing React's internal render processes (not recommended).

React handles rerendering automatically based on changes in state or props. While you can observe when it happens, directly controlling the number of rerenders is not a typical pattern in React.

Question 11/15

😊 Your answer was correct 🙁 Your answer was incorrect

Given the following TypeScript code, what type does the `setColor` function accept?

const [color, setColor] = useState<string | null>(null);

Available answers

Either a string or null.

Only null values.

Only numbers.

Only strings.

The

useState<string | null>

type definition indicates that the state variable and the setter can accept both string and null values.

Question 12/15

😊 Your answer was correct 🙁 Your answer was incorrect

When using a `useReducer` hook in TypeScript, what type parameters should be provided?

type State = {count: number};
type Action = {type: 'increment'} | {type: 'decrement'};

const reducer = (state: State, action: Action): State => {
    switch (action.type) {
        case 'increment':
            return {count: state.count + 1};
        case 'decrement':
            return {count: state.count - 1};
        default:
            return state;
    }
};

Available answers

Only the state type, as action can be inferred.

The state and action types for the reducer function.

Only the action type, as state is self-inferable.

Component props and reducer return type.

In TypeScript,

useReducer

should be provided with both state and action types to ensure type-safety within the reducer logic.

Question 13/15

😊 Your answer was correct 🙁 Your answer was incorrect

In TypeScript, how do you prevent assigning `undefined` to a prop?

interface MyComponentProps {
    name: string;
}

const MyComponent: React.FC<MyComponentProps> = ({ name }) => {
    return <div>Hello, {name}</div>;
};

Available answers

With default parameters in the function implementation.

By initializing the prop with an empty string.

By using `undefined` in the type restriction.

By not using the `?` modifier in the interface declaration.

In TypeScript, to make a parameter non-optional (i.e., prevent it from being

undefined

), you simply omit the

modifier in the type interface definition.

Question 14/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is the purpose of the `React.FC` type in a TypeScript React component?

const MyComponent: React.FC = () => {
    return <div>Hello, World!</div>;
};

Available answers

To declare state in a functional component.

To define a class component.

To handle side effects in a component.

To type the props of a functional component.

React.FC

is a type alias provided by React for defining function components with props in TypeScript.

Question 15/15

😊 Your answer was correct 🙁 Your answer was incorrect

In TypeScript, what is a Discriminated Union and how is it useful in React?

type LoadingState = {
    state: 'loading';
};

type SuccessState = {
    state: 'success';
    response: string;
};

type ErrorState = {
    state: 'error';
    error: Error;
};

interface StateContainer {
    stateObject: LoadingState | SuccessState | ErrorState;
}

const Component: React.FC<StateContainer> = ({ stateObject }) => {
    switch (stateObject.state) {
        case 'loading':
            return <div>Loading...</div>;
        case 'success':
            return <div>{stateObject.response}</div>;
        case 'error':
            return <div>Error: {stateObject.error.message}</div>;
        default:
            return null;
    }
};

Available answers

A type that ignores type safety for the sake of flexibility.

A type that allows multiple inheritance in TypeScript.

An alias for a generic type.

A type that combines multiple types with shared identifiers to allow narrowed type checking based on specific values.

Discriminated Unions in TypeScript are a form of union types that allow complex object typing based on a shared, common property (the discriminant) that acts as an identifier—very useful in component prop interfaces for handling multiple types with known distinctions.