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Main Index
2. How Virtual DOM is different from Real DOM?
5. Can web browsers read a JSX file?
6. What are some of the significant characteristics of React?
7. Why is React widely utilized today?
8. What are disadvantages of using React?
9. How React is different from Angular?
10. What do you know about component-based architecture of React?
11. How does ‘rendering’ perform in React?
12. Do you know ‘states’ in React?
13. Do you know props in React?
14. What is the main utility of an arrow function in React?
15. Describe function of a higher-order component (HOC) in React?
16. What is create-react-app in React?
17. What are benefits of utilizing create-react-app in React?
19. How props is different from states?
Intermediate Interview Questions
20. What are the 3 phases of a component life cycle in React?
22. How can we create events in React?
23. Write difference between routing in React and conventional routing?
24. In React, Find difference between Flux and Redux.
25. Can you use AJAX with React?
26. Describe the synthetic events in React?
27. What do you mean by “refs” in React?
28. What are controlled components in React?
29. Describe stateful components in React.
30. Why is a router necessary in React?
31. What are the drawbacks of MVC in React?
32. Explain about pure components in React?
33. What are the main components of Redux in React?
34. What are the benefits of Redux?
Advanced React Interview Questions.
35. What are main uses of higher-order components (HOCs)?
37. How cloneElement is different from createElement in React?
38. What is the utilization of the 2nd argument that is passed to setState? Is it optional?
39. Is there any approach to avoid the need of binding while utilizing React?
40. How a controlled component is different from an uncontrolled component in React?
41.How we can instruct React to build in the production mode?
42.Do you know StrictMode component that isutilized in React?
43. What would you do if your React app is performing slowly?
44. How getInitialState is different from constructors in React?
45.Which categories of predefined proptypesareavailable in React?
46. Can you include attributes with components conditionallyin React?
47. Why is props passed to the super() function in React?
48. What do you mean by React Fiber?
Introduction
Realizing the quantity of work it needs to overture these interviews, we have
come up with this collection of reactjs interview questions and answers with
the greatest possibility of incident. Going through these significant
questions will provide you the biggest opportunities of replying most of the
reactjs questions asked in a
React.js
interview completely.
Basic level Questions
1. What is React.js?
React.js is a widely utilized
JavaScript
library that was initiated in 2011. It was developed by the highly experienced
developers at Facebook, and it is basically utilized for the purpose of
frontend development. React.js utilizes the component-based method, which
assures to help you develop components that contain high reusability.
React
is mainly popular for designing and developing critical mobile user interfaces
and
web apps.
2. How Virtual DOM is different from Real DOM?
| Virtual DOM | Real DOM |
|---|---|
| Modifications can be done easily | Modifications can be expensive |
| Lesser memory is used. | More memory is used as per demand. |
| JSX element is edited if the element is available | Always creates a new DOM when an element gets edited. |
| It cannot alter HTML directly | It can alter HTML codes directly. |
| Editing will be faster. | Editing will be slower. |
3. Explain Virtual DOM?
A virtual DOM is a basic JavaScript object that is the precise copy of the
related real DOM. You can also consider it as a node tree that includes
elements, attributes, and other additional properties. It develops a node tree
and edits it according to the modifications that arise in the data model
through utilizing the render function of React, . These modifications are
generally triggered by users or the actions induced by the system.
4. What is JSX?
JSX stands for JavaScript
XML. JSX is utilized in React to bring out the significance of JavaScript to
React and utilize it for its benefits.
It even includes bringing out HTML codes and the simple syntax of JavaScript.
This assures that the deriving HTML file will have great readability, thereby
relatively improving the enactment of the application.
Check out the following example of a JSX:
5. Can web browsers read a JSX file?
No, web browsers browsers are not able to read JSX files directly. A web
browser will be able to read only the objects rendered by JavaScript.
Presently, to enable a web browser execute a JSX file, it needs to be
converted to a JavaScript object through JSX transformers, and only then it
can be delivered into the web browser for further utilize in the pipeline.
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6. What are some of the significant characteristics of React?
React has various characteristics that are utilized for different objectives.
Some of them are explained below:
- React utilize a single-way data flow model.
- React utilizes Virtual DOM that has numerous benefits of its own.M
- It helps in comprehensive processing and controlling of server-side
data.er Most in Demand Skills Now !
7. Why is React widely utilized today?
React supplies many advantages to users when developing an app. Some
advantages are given below.
- UI testing is very much easy with React,
- React can be utilized for both server-side and client-side needs.
- We can integrate React with Angular and many frameworks easily.
- The elevated readability index assures of easy perception.
- It improves application enactment and overall performance.
8. What are disadvantages of using React?
There are some constraints while utilizing React as mentioned below:
- Writing code is much complex as it utilizes JSX and inline template
design. - The library encompasses a large repository of data, which might be
irresistible. - Freshers might find it difficult to cope with its procedures and
syntaxes. - React is a simple JavaScript library and not a detailed framework
hence calls for dependencies.
9. How React is different from Angular?
| Angular | React |
|---|---|
| Angular is created by Google. | React is created by Facebook |
| It used Real DOM. | It used Virtual DOM. |
| Its a Client-side program. | Its a Server-side program. |
| You will get absolute MVC support | Only the display aspect of MVC |
| One-way data binding. | Two-way binding. |
10. What do you know about component-based architecture of React?
Generally, components are considered as confoundations in reactjs that are
used to develop user interfaces for apps. Through the component-based system
in position, all of the private entities become totally reusable and
self-reliant of each other. This indicates that providing the app is easy and
not pendant on the different components of the User Interface.
11. How does ‘rendering’ perform in React?
Rendering is a significant characteristic of React as each component must be
provided. This is accomplished utilizing the render() function. Once, you call
the function, it returns a specific element that depicts a DOM component.
Also, it is possible to provide multiple HTML element at a time by
encompassing the HTML tags and sending them through the rendering function.
12. Do you know ‘states’ in React?
States are considered as one of the crucial aspects of React. It is a source
of information or objects that handle characteristics such as component
attitude and rendering. States in React, are utilized to create interactive
and dynamic components.
13. Do you know props in React?
Props are the short name used for full name properties in React. The Props are
generally read-only elements that are inflexible in nature. In an app, props
follow a structure that is sent from parents components to child components.
Nevertheless, the reverse is not endorsed. This is accomplished to assure that
there is only a unique directional progression in information always.
14. What is the main utility of an arrow function in React?
Generally, an arrow function is utilized to compose an expression in Reactjs.
It permits users to manually connect components effortlessly. The utility of
arrow functions can be extremely valuable when you are functioning with
higher-order functions especially.
Example:
15. Describe function of a higher-order component (HOC) in React?
Higher-order components (HOCs) procedures are widely used in React to apply
concepts that include the component reutility logic.
They are not the
React Native Firebase portion of the React API and enable users to reutilize the
code as well as bootstrap abstraction smoothly.
HOCs are also utilized to enable simple sharing of features across all of the
React components , including more advancements to the efficiency and
performance of the app.
16. What is create-react-app in React?
The create-react app is a simple CLI (command-line interface) that is utilized
in the development of React apps, which doesn’t have any development
configuration.
All tools are pre-installed while utilizing the CLI, and this enables users to
concentrate on the code to build the app and no need to focus on dependencies.
The following syntax is utilized to begin a simple project in React:
Create-react-app my-app
17. What are benefits of utilizing create-react-app in React?
Following are benefits of utilizing create-react-app
- Almost developed and ready with auto-prefixed CSS
- Provides facilities for ES6, JSX, and flow statements
- Quick interactive inspecting elements
- Live project development servers which assist in debugging
-
Scripts to deal with
CSS, JSS, and other types of files
18. Define Redux?
Redux is utilized to preserve the state of the app in a single specific
entity. Generally, this simple entity is a JavaScript object. Altering states
can be accomplished by carrying out actions from the app and writing related
objects for them that are utilized to alter the states.
For example:
All of the data is preserved by redux or store.
19. How props is different from states?
| Criterions | Props | States |
|---|---|---|
| Modification in child components | Yes | No |
| Parent component altering values | Yes | No |
| Modifications inside components | No | Yes |
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Intermediate Interview Questions
20. What are the 3 phases of a component life cycle in React?
The 3 phases of the life cycle of a component are as follows.
-
Initial rendering: In this phase, the journey of the component to the DOM is
started. -
Update: In this middle phase, the component can be modified and rendered
again if needed after adding to the DOM. -
Unmounting: In this final phase, the demolition of the component and its
eventual disposal from the DOM are occured.
21. What are events in React?
Whenever the actions are conducted in React, such as drifting the mouse or
pressing any key on the keyboard, these kinds of activities trigger events.
Events then perform set activities as an acknowledgment to these triggers.
Controlling a React event is relatively similar to that within the DOM
architecture.
22. How can we create events in React?
We can create Events in React very easily using following codes.
23. Write difference between routing in React and conventional routing?
-
Pages: In conventional routing, each view is taken as a new file while
in React, it is taken as a single HTML type entity. -
Navigation: The views in React, are not replenished as the objects are
re-issued to make new views.
But, the users need to go through the web pages for watching in case of
conventional routing.
24. In React, Find difference between Flux and Redux..
| Flux | Redux |
|---|---|
| Components related to Flux in React | Storage of components directly relate |
| A dispatcher is available. | No dispatcher is available. |
| Single store is available. | Multiple stores are vailable. |
| Mutable state | Immutable state. |
| Possesses state and logic | State and logic are different. |
25. Can you use AJAX with React?
Yes, we can use any
AJAX library, such as
jQuery AJAX
and Axios. We can use these libraries with React easily. One significant thing
is to retain the components’ states, and the props are also passed from the
parents components to the child components.
Child components cannot send props back to parents, and this factor truly
enhances rendering efficiency while dynamic data is included.
26. Describe the synthetic events in React?
Synthetic events in React are known as objects that act as cross-browser
wrappers, granting the utilization of native events. This is attained to make
sure that different types of web browsers can run the API and that the event
carries all characteristics.
27. What do you mean by “refs” in React?
‘Refs’ stands for references. We can store a reference utilizing ‘Refs’ to a
single React component or element. This is returned later utilizing the render
procedure.
Generally, they are utilized in the following situations:
- To start essential animations
- To attend DOM libraries of third-party.
- To handle focus and execute media playback
28. What are controlled components in React?
In React, the well handled components refer to the specific components that
retains the capability to retain their state. The data is wholly regulated by
the parent component, and the recent value is retrieved by utilizing props.
This is attained to notify about any modification that happens when utilizing
callbacks.
29. Describe stateful components in React.
Stateful components are such entities that keep the modifications that happen
and put the same into the memory. The state can get altered here, alongside
gathering data such as past, recent, and future modifications.
30. Why is a router necessary in React?
In React, a router is very much essential as it is utilized to control
multiple routes whenever an internet user types in a URL. If the route is
available in the router for the same URL, then the user is guided to the
specific route.
To make this possible, the router library should be included in React. It can
be performed through the following syntax:
31. What are the drawbacks of MVC in React?
Some minor issues of MVC are stated below:
- A lot of memory is wasted.
- DOM alteration costs a lot.
- Several dependencies are produced.
- The complicatedness of models rises.
- The app seems to be slow.
32. Explain about pure components in React?
Ans. Pure components are unique entities that are composed in React.
Basically, they are fast and easy to write and capable to replace a component
which retains only the render() procedure. This is accomplished to make sure
that the execution of the app is good and that the code is remained simple at
the same moment.
33. What are the main components of Redux in React?
Redux has 4 main components as follows:
- Action: An object that explain the call
- Reducer: state modification storage unit
- Store: state and object tree repository
- View: Displays data delivered by the store
34. What are the benefits of Redux?
Some crucial benefits of Redux are given below.
Organized method: Redux desires code to get organized, thereby making it
constant and simple to process with.
Testing Ability: Redux functions are small and deserted, enabling the code
more dominant and testable
Community: Redux has a bigger community, assisting users with valuable and
simple libraries.
Tools: Developers can trace actions and all tools in React utilizing Redux
easily.
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Advanced React Interview Questions.
35. What are main uses of higher-order components (HOCs)?
Ans. Following are main uses of HOCs.
- Alteration of props
- State modification and abstraction
- Provide high jacking
- Bootstrap conception
- Code reuse
36. What are keys in React?
Keys are utilized in React to check all items and to trace modifications
vigorously. They are utilized to quickly check if an item has been put in or
eliminated from a list.
Go through the following syntax:
37. How cloneElement is different from createElement in React?
In React, the cloneElement is basically utilized to clone an element and send
it to new props immediately. Whereas, createElement is such entity that JSX
gets assembled into. This is also utilized to develop elements in React.
38. What is the utilization of the 2nd argument that is passed to setState? Is it optional?
In React, when setState is completed, a callback function is mustered, and the
components get re-rendered.
Yes, it is a discretionary statement. Since setState is asynchronous, it
carries another callback function. Nevertheless, in programming method, it is
often good to utilize another life cycle procedure instead of this.
39. Is there any approach to avoid the need of binding while utilizing React?
Yes, you can utilize two main approaches to prevent the necessity of
binding.
They are as follows:
- Specifying the Event controller as an Inline Arrow procedure:
- Utilizing a procedure component along with Hooks:
Also, the Event Handler can be distinguished as an Arrow procedure, which is
ultimately allocated to a Class Field to get similar results.
40. How a controlled component is different from an uncontrolled component in React?
A controlled component is such a component which is completely controlled by
React. It is the unique point of data for the development forms.
The form data of an uncontrolled component gets controlled by DOM and not by
the component of the React . This is generally accomplished through refs in
React.
41. How we can instruct React to build in the production mode?
We can code in React to develop by putting the process.env.NODE_ENV variable
into production.
Note: While React is in development, warnings and different development
characteristics are not disclosed.
42. Do you know StrictMode component that isutilized in React?
The StrictMode component whileutilized would support users awfully while
building new codebases to realize the components being utilized.
Nevertheless, it can fit well in debugging as well as it helpsresolve the
issuesfaster when it is tied with other components, which could be resulting
in the difficulty.
43. What would you do if your React app is performing slowly?
The cause of slow performance in React is mainly because of the number of
re-renderingprocedures, which are sometimes not necessary. The two major tools
contributed by React to assist users here:
-
memo(): This helps in prevent all of the useless re-rendering accomplished
by the function components. -
PureComponent: This makes sure that the needless re-rendering of class
components is prevented.
44. How getInitialState is different from constructors in React?
While utilizing ES6, the users need to commence the state in the builder and
the getInitialState procedure is initiated. This is accomplished through
React.createClass as given in the below example:
This above code is sameas the following:
45. Which categories of predefined proptypesareavailable in React?
The five main predefined prop categories in React are as follows
- PropTypes.bool
- PropTypes.number
- PropTypes.func
- PropTypes.node
- PropTypes.string
The propTypes can be specified for the user component as given below:
46. Can you include attributes with components conditionally in React?
Yes, there is an option in which we can include attributes with a React
component when such conditions are fulfilled. Also, React can omit an
attribute if a true value is not passed to it.
Go through the following example:
47. Why is props passed to the super() function in React?
We pass Props onto the super() function if a user wants to connect this.props
in the constructor.
Go through the following example:
48. What do you mean by React Fiber?
React Fiber is a latest engine in React and it is known as the implemented
core algorithm in React 16.
The main objective of React Fiber is to make sure that there are accumulative
rendering services for the virtual type DOM. This boosts capacities while
providing gestures, animations, etc. and also assists in assigning preference
to updates based on the necessities, thereby improving overall efficiency.
49. Define Hooks in React?
Hooks help in utilization of the state and other characteristics without
writing a class explicitly. Hooks were included in the React version16.8. So,
the stateful logic can be taken out from a component effortlessly, alongside
inspecting and reutilizing it. All of this is accomplished without modifying
the component structure.
Conclusion
Hope, with the above reactjs interview questions and answers, the candidates
will be able to pass the technical interview steps. It is often
beneficial to get a certification in the technology that you’re seeking for.
By including a lot of value to your cv and knowledge on the above topic, it
can be utilized to achieve a well-coveted professional job in the industry!
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