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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 merging objects in the component.

By creating a utility type.

By using `implements` keyword.

By using the `extends` keyword.

Question 2/15

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

By initializing the prop with an empty string.

By using `undefined` in the type restriction.

Question 3/15

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

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

Using state variables to count rerenders manually within the component.

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

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

Question 4/15

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

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

Select your answer

useState

useContext

useReducer

useEffect

Question 5/15

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.

An alias for a generic type.

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

A type that allows multiple inheritance in TypeScript.

Question 6/15

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 an `Optional` type alias.

By using `undefined` in the prop type.

By using `?` after the prop name.

Question 7/15

How do you define default props in a React component using TypeScript?

interface MyComponentProps {
    name?: string;
}

const MyComponent = ({ name = "Guest" }: MyComponentProps) => {
    return <div>Hello, {name}</div>;
};

Select your answer

Using `static defaultProps` in a class component.

Using `MyComponent.defaultProps`.

Directly in the JSX return statement.

Using default parameter syntax in the props destructuring.

Question 8/15

Which TypeScript utility can you use to define only some of the properties of an interface as required?

interface Person {
    name: string;
    age: number;
    address?: string;
}

const person: Required<Pick<Person, 'name' | 'age'>> = { name: 'Alice', age: 30 };

Select your answer

`Partial` and `Omit` combined.

`Readonly` and `Mutable`.

`Pick` and `Required` combined.

`Optional` and `Strict`.

Question 9/15

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 disable an item in a list.

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

To create a reference pointer for each element.

To set a unique id for each HTML element.

Question 10/15

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

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

Select your answer

Only numbers.

Only null values.

Only strings.

Either a string or null.

Question 11/15

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

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

Annotating the component as `React.AsyncComponent`.

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

Declaring the function inside `useEffect`.

Question 12/15

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.

Use dynamic prop types with the `any` type.

Directly declare types in the function body after JSX.

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

Question 13/15

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 define a class component.

To handle side effects in a component.

To declare state in a functional component.

To type the props of a functional component.

Question 14/15

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

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

Create it as a standalone JavaScript function without types.

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

Declare it as a class method for managing state.

Question 15/15

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 `JSX.Element`.

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

By defining the prop type as `ReactElement`.

By defining the prop type as `Element`.

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 merging objects in the component.

By creating a utility type.

By using `implements` keyword.

By using the `extends` keyword.

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

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

By initializing the prop with an empty string.

By using `undefined` in the type restriction.

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 3/15

😊 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

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

Using state variables to count rerenders manually within the component.

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 4/15

😊 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

useContext

useReducer

useEffect

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 5/15

😊 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.

An alias for a generic type.

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

A type that allows multiple inheritance in TypeScript.

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.

Question 6/15

😊 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 an `Optional` type alias.

By using `undefined` in the prop type.

By using `?` after the prop name.

In TypeScript, you can make a prop optional by adding

after the prop name in the interface.

Question 7/15

😊 Your answer was correct 🙁 Your answer was incorrect

How do you define default props in a React component using TypeScript?

interface MyComponentProps {
    name?: string;
}

const MyComponent = ({ name = "Guest" }: MyComponentProps) => {
    return <div>Hello, {name}</div>;
};

Available answers

Using `static defaultProps` in a class component.

Using `MyComponent.defaultProps`.

Directly in the JSX return statement.

Using default parameter syntax in the props destructuring.

In TypeScript, you can set default values for props by using default parameter syntax during destructuring of the props argument.

Question 8/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which TypeScript utility can you use to define only some of the properties of an interface as required?

interface Person {
    name: string;
    age: number;
    address?: string;
}

const person: Required<Pick<Person, 'name' | 'age'>> = { name: 'Alice', age: 30 };

Available answers

`Partial` and `Omit` combined.

`Readonly` and `Mutable`.

`Pick` and `Required` combined.

`Optional` and `Strict`.

The

Pick

utility allows you to select a subset of properties, and the

Required

utility enforces the selected properties to be required.

Question 9/15

😊 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 disable an item in a list.

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

To create a reference pointer for each element.

To set a unique id for each HTML element.

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 10/15

😊 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

Only numbers.

Only null values.

Only strings.

Either a string or null.

The

useState<string | null>

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

Question 11/15

😊 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

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

Annotating the component as `React.AsyncComponent`.

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

Declaring the function inside `useEffect`.

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

() => Promise<void>

to indicate it returns a promise resolving void.

Question 12/15

😊 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.

Use dynamic prop types with the `any` type.

Directly declare types in the function body after JSX.

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 13/15

😊 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 define a class component.

To handle side effects in a component.

To declare state in a functional 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 14/15

😊 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

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

Create it as a standalone JavaScript function without types.

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

Declare it as a class method for managing state.

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 15/15

😊 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 `JSX.Element`.

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

By defining the prop type as `ReactElement`.

By defining the prop type as `Element`.

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.