How does React remember which state variable belongs to which useState call?

It traverses the calls again, whenever needed

How many calls can we make to useState or useEffect in a single component?

Unlimited, but equal calls for both hooks

Limited, but equal calls for both hooks

When should you use the useEffect hook?

When you want to trigger a side effect

When you need to manage component state

When you need to memoize expensive function results

When you need to optimize rendering performance

How does the useEffect hook improve performance?

By reducing the number of component re-renders

By handling asynchronous operations more efficiently

By optimizing the component's memory usage

By providing a clean way to handle side effects

Can the useEffect hook be used to perform data fetching?

Yes, it's a recommended approach for data fetching

No, useEffect is only for managing component state

Yes, but only once in a project

Data fetching should be done outside of useEffect

What happens if you omit the dependency array in the useEffect hook?

The effect will run on every render

The effect will run once after the initial render

What is the purpose of returning a cleanup function in useEffect?

To clean up after the effect has been applied

To cancel the effect before it's finished

To prevent memory leaks caused by the effect

To control the order of effect execution

Can you use async/await inside the callback function of useEffect?

Yes, it's a recommended approach

No, async/await should not be used inside useEffect

It depends on the scope and scale of the project

Async/await is not supported in useEffect

How can you provide a default value to a context using the createContext function in React.js?

By passing a default value to the createContext function

By using the defaultValue prop in the Context.Provider

By passing the default value directly to the useContext hook

By setting a default value using the useContextDefault method

How can you access the context value outside of the render function in a functional component?

Creating a separate custom hook

Storing the context value in a global variable

Context values can only be accessed within the render function

How can you update the context value dynamically using the useContext hook?

By updating the value provided by the context provider

Context values are immutable and cannot be updated

When should you use the useRef hook?

When you need to reference a DOM element

When you need to manage component state

When you want to trigger a side effect

When you need to optimize rendering performance

What problem does the useRef hook solve?

Accessing and managing DOM elements

Improving component performance

Managing asynchronous operations

When should you avoid using the useRef hook?

When you need to manage component state

When you want to trigger a side effect

When you need to reference a DOM element

When you need to optimize rendering performance

What is the main benefit of using useRef for referencing DOM elements?

It allows safe access and manipulation of DOM elements

It automatically updates the DOM elements

What problem does the useCallback hook solve?

Avoiding unnecessary re-renders

Improving component performance

Managing asynchronous operations

How does the useMemo hook improve performance?

By reducing the number of component re-renders

By handling asynchronous operations more efficiently

By optimizing the component's memory usage

By simplifying the component's lifecycle methods

What happens if you omit the dependencies array in the useMemo hook?

The function will always be memoized

The function will never be memoized

How do "action" and "action creator" differ in Redux?

"Action" is an object describing an event, while "action creator" is a function that returns that object.

"Action" is a function, while "action creator" is an object describing an event.

"Action" and "action creator" are synonymous terms.

"Action" and "action creator" are unrelated.

What can Redux Middleware do in the action processing chain?

Provide a way to handle asynchronous actions and intercept actions before they reach reducers.

Only intervene in sending actions to reducers.

Only handle actions after they have been processed by reducers.

Directly handle actions before they are sent to the store.

How can you combine multiple reducers into a single reducer in Redux?

Using combineReducers from the Redux library.

Manually creating a combined reducer without a library.

Using the reduce method on an array of reducers.

Redux does not support combining multiple reducers.

How do you handle asynchronous actions in Redux?

By using middleware like redux-thunk or redux-saga.

By using synchronous action creators with dispatch.

By writing asynchronous logic directly inside reducers.

Redux does not support asynchronous actions.

In the context of Redux, what are "selectors" and how do they enhance performance?

Selectors are functions that compute derived data from the Redux store, and they enhance performance by memoizing the results to avoid recalculating on every render.

Selectors are middleware functions that intercept and modify actions before they reach reducers.

Selectors are methods of the Redux store that directly update the state based on specific conditions.

Selectors are used to dispatch actions based on the current state of the store.

What will the code do?

It will create two props, increment and decrement, that dispatch the corresponding actions.

It will create two props, increment and decrement, that update state directly.

It will create a single prop that dispatches both actions.

It will create two props, but they won't work correctly with Redux.

Given the following reducer, what will the state be after calling the action SET_NAME with the payload { name: 'Alice' }?

{ name: 'Alice', age: undefined }

{ name: 'Alice', name: 'Alice' }

What is the result of using useCallback with an empty dependency array? const memoizedCallback = useCallback(() => { console.log('Callback'); }, []);

The callback will be the same across renders.

The callback will be recreated on every render.

The callback will be recreated only when dependencies change.

The callback will never execute.

How does useReducer differ from useState?

useReducer is used for complex state logic, while useState is for simple state management.

useReducer manages side effects, while useState handles state.

useReducer requires a class component, while useState does not.

What is the main purpose of combineReducers in Redux?

To combine multiple reducers into a single reducer function.

To merge multiple action creators.

ReactJS OVerview Unit 11-18

Authored by Hiếu Nguyễn

Information Technology (IT)

Professional Development

Used 4+ times

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50 questions

Show all answers

MULTIPLE SELECT QUESTION

45 sec • 1 pt

Which of the following is true regarding Babel ? (2 correct answers)

A compiler

A transpiler

A framework

A programming language

MULTIPLE CHOICE QUESTION

45 sec • 1 pt

What "_____case" does React DOM use for naming attributes and properties?

Camel (camelCase)

Pascal (PascalCase)

Snake (snake_case)

Kebab (kebab-case)

MULTIPLE CHOICE QUESTION

45 sec • 1 pt

What are the smallest building blocks of React apps

Components

Functions

Elements

JSX

MULTIPLE CHOICE QUESTION

45 sec • 1 pt

A component name must start with ________.

a lowercase letter

a capital letter

a number

everything

MULTIPLE CHOICE QUESTION

45 sec • 1 pt

Which component lifecycle method runs after the component output has been rendered to the DOM?

componentMounted()

componentRendered()

componentDidMount()

componentDidRender()

MULTIPLE CHOICE QUESTION

45 sec • 1 pt

Which component lifecycle method is used to perform the cleanup when the component is removed from the DOM?

componentUnmounted()

componentWillUnmount()

componentDidUnmount()

None of the above

MULTIPLE CHOICE QUESTION

45 sec • 1 pt

State of a component is often called ___ data?

public

protected

private

local or encapsulated

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ReactJS OVerview Unit 11-18

Which of the following is true regarding Babel ? (2 correct answers)

What "_____case" does React DOM use for naming attributes and properties?

What are the smallest building blocks of React apps

A component name must start with ________.

Which component lifecycle method runs after the component output has been rendered to the DOM?

Which component lifecycle method is used to perform the cleanup when the component is removed from the DOM?

State of a component is often called ___ data?

In order to prevent a component from rendering it should return ___?

Which of the following activities do we perform while declaring useState in React?

How does React remember which state variable belongs to which useState call?

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