react

Question 1

What is React?

Answer 1

A JavaScript library for building user interfaces or UI components

Question 2

What is a React element?

Answer 2

an object describing a component instance or DOM node and its desired properties

Question 3

How do you mount a React element to the DOM?

Answer 3

ReactDOM.render(element, container)

Question 4

What is Babel?

Answer 4

Babel is a toolchain that is mainly used to convert ECMAScript 2015+ code into a backward-compatible version of JavaScript in current and older browsers or environments.

Question 5

What is a Plug-in?

Answer 5

is a software component that adds a specific feature to an existing computer program.

Question 6

What is a Webpack loader?

Answer 6

Loaders are transformations that are applied to the source code of a module.

Question 7

How can you make Babel and Webpack work together?

Answer 7

by adding babel-loader to the list of modules in webpack.config

Question 8

What is JSX?

Answer 8

A syntax extension of JavaScript.

Question 9

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

Answer 9

Becasue the React library must be in scope from the JSX code in order to make calls to React.createElement

Question 10

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

Answer 10

by installing the react plugin

Question 11

What is a React component?

Answer 11

a JavaScript class or function that optionally accepts inputs i.e. properties(props) and returns a React element that describes how a section of the UI (User Interface) should appear.

Question 12

How do you define a function component in React?

Answer 12

By writing a JavaScript function that accepts props as a single argument and returns a React element

Question 13

How do you mount a component to the DOM?

Answer 13

ReactDOM.render( )

Question 14

What are props in React?

Answer 14

They are objects used to pass data between react components

Question 15

How do you pass props to a component?

Answer 15

ComponentName (props)

Question 16

How do you write JavaScript expressions in JSX?

Answer 16

wrap it in { } curly braces

Question 17

How do you create “class” component in React?

Answer 17

class ComponentName extends React.Component {
    render ( ) {
         return....
        }
    }

Question 18

How do you access props in a class component?

Answer 18

this.props

Question 19

What is the purpose of state in React?

Answer 19

State is an object where property values belonging to a component are stored. When state changes, the componenet re-renders

Question 20

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

Answer 20

as an attribute

Question 21

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

Answer 21

map

Question 22

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

Answer 22

id or anything unique

Question 23

What are controlled components?

Answer 23

An input form element whose value is controlled by React. The React component that renders a form also controls what happens in that form on subsequent user input.

Question 24

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

Answer 24

value and onChange / handleSubmit and handleChange

Question 25

When does React call a component’s componentDidMount method?

Answer 25

immediately after a component is inserted into the DOM tree. after the render phase

Question 26

Name three React.Component lifecycle methods.

Answer 26

constructor, render, componentDidMount

Question 27

How do you pass data to a child component?

Answer 27

props