This set of Multiple Choice Questions & Answers (MCQs) focuses on “React JS”.
1. What is React.js?
a) Open-source JavaScript back-end library
b) JavaScript front-end library to create a database
c) Free and open-source JavaScript front-end library
d) None of the mentioned
View Answer
Explanation: React.js is a free and open-source JavaScript front-end library for creating user interfaces and UI components. It’s also referred to as React or ReactJS.
2. Which of the following acts as the input of a class-based component?
a) Class
b) Props
c) Factory
d) None of the mentioned
View Answer
Explanation: React allows users to pass information to a Component using props. Props are kind of global variable or object.
3. React.js is written in which of the following language?
a) C
b) C++
c) JavaScript
d) Java
View Answer
Explanation: React Native is built on a JavaScript based React.js framework. This is a significant benefit, given that JavaScript is such a widely used language.
4. How many elements can a valid react component return?
a) React doesn’t return element
b) 1 Element
c) More than 1 element
d) None of the mentioned
View Answer
Explanation: A valid react component can return only one element.
5. In which of the following directory React Components are saved?
a) Inside js/components/
b) Inside components/js/
c) Inside vendor/js/components/
d) Inside vendor/components/
View Answer
Explanation: Inside js/components/ directory React Components are saved.
6. Which of the following command is used to Install create-react-app?
a) npm install create-react-app
b) npm install -f create-react-app
c) npm install -g create-react-app
d) install -g create-react-app
View Answer
Explanation: The “npm install -g create-react-app” command is used to install the create-react-app.
7. In which condition is the React.js Lifecycle method static getDerivedSateFromProps(props, state) is called?
a) When the state of the component is updated
b) When a component is created for the first time
c) Both of the mentioned
d) None of the mentioned
View Answer
Explanation: In React. js, the static getDerivedSateFromProps(props, state) is called in both the cases when a component is created and when a component is updated.
8. Which of the following is method is not a part of ReactDOM?
a) ReactDOM.hydrate()
b) ReactDOM.destroy()
c) ReactDOM.createPortal()
d) All of the mentioned
View Answer
Explanation: ReactDOM.destroy() method is not a part of ReactDOM. ReactDOM provides the developers with an API containing the methods such as render(), findDOMNode(), unmountComponentAtNode(), hydrate(), and createPortal().
9. Which of the following is correct about prop in react?
a) Can be changed inside another component
b) Can be changed inside the component
c) Cannot be changed in the component
d) All of the mentioned
View Answer
Explanation: Props cannot be changed, they are immutable. A prop is a special keyword, that stands for properties.
10. Which of the following is used to pass data to a component from outside in React?
a) props
b) render with arguments
c) setState
d) PropTypes
View Answer
Explanation: Props can be used to pass dynamic data to a component. When the data in the props changes, the component re-renders.
Sanfoundry Global Education & Learning Series – Javascript Programming.
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