React + Node + Next.js UPDATED ACTUAL
Exam Questions and CORRECT Answers
What are the differences between the Real DOM and the Virtual DOM? - CORRECT
ANSWER - 1. The Virtual DOM updates faster than the Real DOM.
2. The Real DOM can directly update HTML whereas the Virtual DOM can't.
3. The Real DOM creates a new DOM when an element updates whereas the Virtual DOM
updates the JSX.
4. DOM manipulation with the Virtual DOM is much less expensive than with the Real DOM.
How does the Virtual DOM work? - CORRECT ANSWER - When there is a change in
state that affects the DOM, React first updates the Virtual DOM to reflect this change. Two
Virtual DOMs exist for each React app, one of which stores a representation of the DOM after
these updates while the other one stores a representation of the DOM before the updates.
React then uses a process called reconciliation to create a diff of the two Virtual DOMs by
comparing them. Every difference between the two is then rendered in the Real DOM which
allows us to update only the elements that have changed instead of re-rendering the entire Real
DOM which can be pretty expensive and inefficient.
What is React? - CORRECT ANSWER - React is an open source front-end JavaScript
library developed by Facebook in 2011. It follows a component based approach which allows us
to create reusable UI components.
What are the features of React? - CORRECT ANSWER - 1. It uses the Virtual DOM to
handle updates and changes in state.
2. It supports server-side rendering.
,3. It follows unidirectional data flow.
4. Uses reusable/composable UI components.
What is server-side rendering? - CORRECT ANSWER - Server-side rendering is the
process of taking a client-side JavaScript framework website and rendering it to static HTML
and CSS on the server.
This is a tool to get the website to render faster. With server-side rendering, you can generate the
HTML on the server and send that to the browser so that the user can see the HTML version of
the app almost immediately as the JS app boots up in the background. At this point, the app will
be visible to the user but not interactive until the JS is parsed and executed. There are ways in
which this can be set up (e.g. using a cache) in order to make the TTI (time to interactive)
quicker.
List some of the major advantages of React. - CORRECT ANSWER - 1. The use of the
Virtual DOM improves efficiency.
2. Server-side rendering can boost the SEO of an app.
3. Reusable components increase the pace of development since they can be composed and even
shared across different apps.
4. There is a huge ecosystem of libraries and tools to choose from that can be integrated into
React apps.
What is JSX? - CORRECT ANSWER - JSX is a shorthand for JavaScript XML. This is a
type of file used by React which utilizes the expressiveness of JavaScript along with HTML like
template syntax.
Why can't browsers read JSX? What is the process that allows it to be read? - CORRECT
ANSWER - Browsers can only read JavaScript objects but JSX in not a regular JavaScript
, object. Thus to enable a browser to read JSX, first, we need to transform JSX file into a
JavaScript object using JSX transformers like Babel and then pass it to the browser.
Explain the statement "in React, everything is a component". - CORRECT ANSWER -
The building blocks of a React application's UI are called components. Any app UI created using
React is divisible into a number of small independent and reusable pieces, known as components.
React renders each of the components independent of each other. Hence, there is no effect of
rendering a component on the rest of the app UI.
What is the purpose of render() in React? - CORRECT ANSWER - Each React component
must have a render() method. It returns a single React element which is the representation of the
native DOM component. If more than one HTML element needs to be rendered, then they must
be grouped together inside one enclosing tag. This function must be kept pure i.e., it must return
the same result each time it is invoked.
What are props? - CORRECT ANSWER - Props are inputs to components. They are
single values or objects containing a set of values that are passed to components on creation
using a naming convention similar to HTML-tag attributes. They are data passed down from a
parent component to a child component.
What is state in React and how is it used? - CORRECT ANSWER - State of a component
is an object that holds some information that may change over the lifetime of the component.
State is similar to props, but it is private and fully controlled by the component. i.e, It is not
accessible to any component other than the one that owns and sets it.
How do you update the state of a component? - CORRECT ANSWER - We must use
this.SetState({ key: value }) to update the state since this function makes the component re-
render to represent the new state. Using this.state.key = value will not re-render the component
so the state change won't be reflected to the user.
What are the phases of a React component's lifecycle? - CORRECT ANSWER - The
component lifecycle has three distinct lifecycle phases:
Exam Questions and CORRECT Answers
What are the differences between the Real DOM and the Virtual DOM? - CORRECT
ANSWER - 1. The Virtual DOM updates faster than the Real DOM.
2. The Real DOM can directly update HTML whereas the Virtual DOM can't.
3. The Real DOM creates a new DOM when an element updates whereas the Virtual DOM
updates the JSX.
4. DOM manipulation with the Virtual DOM is much less expensive than with the Real DOM.
How does the Virtual DOM work? - CORRECT ANSWER - When there is a change in
state that affects the DOM, React first updates the Virtual DOM to reflect this change. Two
Virtual DOMs exist for each React app, one of which stores a representation of the DOM after
these updates while the other one stores a representation of the DOM before the updates.
React then uses a process called reconciliation to create a diff of the two Virtual DOMs by
comparing them. Every difference between the two is then rendered in the Real DOM which
allows us to update only the elements that have changed instead of re-rendering the entire Real
DOM which can be pretty expensive and inefficient.
What is React? - CORRECT ANSWER - React is an open source front-end JavaScript
library developed by Facebook in 2011. It follows a component based approach which allows us
to create reusable UI components.
What are the features of React? - CORRECT ANSWER - 1. It uses the Virtual DOM to
handle updates and changes in state.
2. It supports server-side rendering.
,3. It follows unidirectional data flow.
4. Uses reusable/composable UI components.
What is server-side rendering? - CORRECT ANSWER - Server-side rendering is the
process of taking a client-side JavaScript framework website and rendering it to static HTML
and CSS on the server.
This is a tool to get the website to render faster. With server-side rendering, you can generate the
HTML on the server and send that to the browser so that the user can see the HTML version of
the app almost immediately as the JS app boots up in the background. At this point, the app will
be visible to the user but not interactive until the JS is parsed and executed. There are ways in
which this can be set up (e.g. using a cache) in order to make the TTI (time to interactive)
quicker.
List some of the major advantages of React. - CORRECT ANSWER - 1. The use of the
Virtual DOM improves efficiency.
2. Server-side rendering can boost the SEO of an app.
3. Reusable components increase the pace of development since they can be composed and even
shared across different apps.
4. There is a huge ecosystem of libraries and tools to choose from that can be integrated into
React apps.
What is JSX? - CORRECT ANSWER - JSX is a shorthand for JavaScript XML. This is a
type of file used by React which utilizes the expressiveness of JavaScript along with HTML like
template syntax.
Why can't browsers read JSX? What is the process that allows it to be read? - CORRECT
ANSWER - Browsers can only read JavaScript objects but JSX in not a regular JavaScript
, object. Thus to enable a browser to read JSX, first, we need to transform JSX file into a
JavaScript object using JSX transformers like Babel and then pass it to the browser.
Explain the statement "in React, everything is a component". - CORRECT ANSWER -
The building blocks of a React application's UI are called components. Any app UI created using
React is divisible into a number of small independent and reusable pieces, known as components.
React renders each of the components independent of each other. Hence, there is no effect of
rendering a component on the rest of the app UI.
What is the purpose of render() in React? - CORRECT ANSWER - Each React component
must have a render() method. It returns a single React element which is the representation of the
native DOM component. If more than one HTML element needs to be rendered, then they must
be grouped together inside one enclosing tag. This function must be kept pure i.e., it must return
the same result each time it is invoked.
What are props? - CORRECT ANSWER - Props are inputs to components. They are
single values or objects containing a set of values that are passed to components on creation
using a naming convention similar to HTML-tag attributes. They are data passed down from a
parent component to a child component.
What is state in React and how is it used? - CORRECT ANSWER - State of a component
is an object that holds some information that may change over the lifetime of the component.
State is similar to props, but it is private and fully controlled by the component. i.e, It is not
accessible to any component other than the one that owns and sets it.
How do you update the state of a component? - CORRECT ANSWER - We must use
this.SetState({ key: value }) to update the state since this function makes the component re-
render to represent the new state. Using this.state.key = value will not re-render the component
so the state change won't be reflected to the user.
What are the phases of a React component's lifecycle? - CORRECT ANSWER - The
component lifecycle has three distinct lifecycle phases:
