React

Question 1

What is React?

Answer 1

a javascript library for building user interfaces

Question 2

What is a React element?

Answer 2

an object that describes an element

Question 3

How do you mount a React element to the DOM?

Answer 3

ReactDOM.render()

Question 4

What is JSX?

Answer 4

syntax extension to JavaScript

Question 5

Why must the React object be imported when authoring JSX in a module?

Answer 5

Since JSX compiles into calls to React.createElement, the React library must also always be in scope from your JSX code

Question 6

How can you make Webpack and Babel work together to convert JSX into valid JavaScript?

Answer 6

npm install @babel/plugin-transform-react-jsx

Question 7

What is a React component?

Answer 7

a JavaScript class or function that returns a React element

Question 8

How do you define a function component in React?

Answer 8

function functionName( [props] ) {
return [prop]
}

Question 9

How do you mount a component to the DOM?

Answer 9

ReactDOM.render( element, parent )

Question 10

What are props in React?

Answer 10

When React sees an element representing a user-defined component, it passes JSX attributes and children to this component as a single object. We call this object “props”.

Question 11

How do you write JavaScript expressions in JSX?

Answer 11

{ }

Question 12

How do you create “class” component in React?

Answer 12

define a class that extends Component and has a render method

Question 13

How do you access props in a class component?

Answer 13

this.props

Question 14

What is the purpose of state in React?

Answer 14

to represent information about the component’s current situation to determine behavior

Question 15

How to you pass an event handler to a React element?

Answer 15

assign it to the elements prop using { }

Question 16

What are controlled components?

Answer 16

A controlled component is a component that renders form elements and controls them by keeping the form data in the component’s state

Question 17

What two props must you pass to an input for it to be “controlled”?

Answer 17

value and onChange

Question 18

What Array method is commonly used to create a list of React elements?

Answer 18

map

Question 19

What is the best value to use as a “key” prop when rendering lists?

Answer 19

Unique IDs

Question 20

When does React call a component’s componentDidMount method?

Answer 20

right after the component has been mounted on the tree

Question 21

Name three React.Component lifecycle methods.

Answer 21

componentDidMount(), componentDidUpdate(), componentWillUnmount()

Question 22

How do you pass data to a child component?

Answer 22

as a prop