ReactJS Interview Questions and Answers
Reactjs is a JavaScript library used for building reusable user interface components. It was developed by Facebook alongside other companies in 2013 but has today caught the interest of developers across the globe thanks to its ability to create high-performance, scalable, and simple applications. If the React front-end developer salary of $ 125,050 per annum is anything to go by, React clinches the top spot for the most valued front-end library. Yet, it is one thing to build and master this widely used library and quite another to get through Reactjs interview questions and impress the panel.
As we all may agree, a good candidate prepares adequately for the interview well in advance. This is not merely to get into that position but is also a demonstration of practical knowledge and that you can implement this knowledge to make a meaningful difference in your capacity as a developer qualified in React library.
Frequent ReactJS interview questions and answers
Should you expect tough or technical React interview questions?
This entirely depends on you as an individual. However, interviews have surprised experts therefore through preparation cannot be underestimated. This is why we have compiled 15 frequently asked React interview questions to help you with your preparation.
- What are the features of Reactjs?
The main features that distinguish Reactjs include
- JSX, a JavaScript syntax that resembles XML or HTML
- Multiple reusable components
- Unidirectional data flow also known as one-way data binding
- Virtual DOM, a lightweight virtual representation of the real DOM.
- Explain components in Reactjs?
Components are the basic unit of Reactjs applications. They are reusable and independent. A single React application usually has multiple components. When developing a UI, the various elements of design are broken down into reusable components that can be used to develop other UIs thus eliminating the need to write code from scratch. The advantages of reusable components include fewer bugs and fast development.
- Differentiate between functional and class components in Reactjs.
Reactjs components are divided into two categories, functional components and class components.
Functional components are stateless components whose function is to take props as a parameter and return a React element. They are easy to read, test, debug and deliver greater capability for reusability.
Class components, on the other hand, have a state and render method thus allowing developers to implement state and logic. They are also known as stateful components.
- What are pure components in Reactjs?
In Reactjs, pure components are those whose output is determined by their input, in this case, props. Pure components are used to optimize the performance of an application as they are fast to write and will not modify the state or props of values.
- Explain stateless components
Stateless components are those components that do not possess their own states thus taking the form applied to them via props.
- Explain the difference between state and props in Reactjs
The state of a component refers to the elements that define the functions and characteristics of the component in the Reactjs application and is created inside the component. Once integrated into a React application, the start point of a state is a default value. With time as user events occur, the value of the state of a component is updated in line with the events.
Props, on the other hand, are configurations transferred from a parent component to a PureComponent as input values. Props can be single values or objects that possess a group of values passed on to the child components. The props of a component cannot be changed.
- When are refs used in Reactjs?
Reactjs provides refs as tools for accessing the DOM and React elements from within the component and modifying the value of a child component without making use of the props. In this case, the user is only required to attach a ref to the element in the application to enable access.
- Is HTML used in Reactjs?
No.
Reactjs uses JSX, a syntax extension of JavaScript. JSX stands for JavaScript XML. It allows users to write HTML in React to create React elements when building user interfaces for applications.
- What is Redux and what are its constituent components?
Redux is a Reactjs library that is used during front-end development to write JavaScript applications. Redux is used for managing and storing an application’s state in a single central store such that each component accesses a specific state from this same store.
Redux comprises three components
- Actions are events or the way through which information is sent from the application to the store using store.dispatch() method. They act and are the single source of data for the store.
- Reducers, based on the reduce function in JavaScript, are functions that determine the new state of an application after an action sent to the store is performed on it.
- The store contains the new states that are stored as JavaScript objects and are updated by performing actions on applications and reducers for these actions written to modify the state using dispatch (action):
It is important to note that Redux can only have a single store.
- Name the features of Redux Workflow
- Reset: Resets the state of the store
- Revert rolls back the last committed state
- Sweep eliminates all disabled actions
- Commit saves the current state as the initial state to which the revert will return.
- What benefits does Redux offer?
- Redux offers centralized and more effective management of states in the store particularly for large complex applications with multiple components.
- It is easy to predict state with Redux based on the pure functions of the Reducer
- Redux optimizes React application performance as components re-render only when its data is changed.
- Redux has persistent data storage capabilities which is a plus as the data persists until the page is refreshed when navigating a user interface.
- Redux makes time-travel debugging of applications fast and easy
- Redux has a strict code organization and structure which makes its maintenance easy
- What is the difference between DOM and Virtual DOM?
DOM stands for document object model and represents an abstraction of a structured text displayed by HTML code. Thus DOM is simply referred to as HTML DOM.
Virtual DOM on the other hand is an abstraction of HTML DOM hence an abstraction of an abstraction. In React, there is a lightweight virtual DOM for every DOM Object. React performs computations faster in the Virtual DOM as nothing is changed on the screen. Manipulating the real DOM is often a slow process.
- What is the importance of the render() function in Reactjs?
The render() function in React is used to update the user interface. Each Reactjs component has a render() function that when sent to ReactDOM returns a new React element. The new Reactjs element created is a representation of the DOM component and is immutable.
- Does Reactjs have limitations?
Some of the limitations of ReactJS are:
- Reactjs is designed to handle only the UI layers of an application. Thus a combination of technologies is required for developing a complete application.
- Reactjs uses JSX, a JavaScript syntax extension that allows users to write HTML in JavaScript. Some developers, particularly those that are new in the industry, find this complex and as such, a barrier to development with Reactjs.
- Reactjs features highly detailed documentation and manuals that users new to React often find difficult to understand and implement.
- React has too wide a library.
- What is NPM and why is it used for web development in Reactjs?
NMP stands for Node Package Manager. It is the default package manager for Nodejs and is written in JavaScript. It is made up of a command-line interface (CLI) and the NPM registry which makes it easy to install any packages in the registry using the NPM CLI.
Conclusion
Since its release, React has seen such active development thus growing to become one of the most widely utilized frontend libraries for enterprise applications. It has revolutionized the development of component-based application architecture in an era where optimized performance says loads about an application. With regular updates and improvements, this library has proved to be the most treasured tool in the developer’s toolset. The bottom line is, React skills are today the most demanded and rewarded among developers.