Choosing the right technology for a new app or website is getting more complex. One of the fastest-growing Javascript frameworks is React. React certification has seen steady growth in demand as JavaScript technologies have gained traction in the market. React’s a low learning curve, reusable components, and clean abstraction make it an obvious choice for front-end developers throughout the globe. We’ve collected a list of some of the most typical React interview questions and answers to assist you in your preparation.
Listed here are 10 of the most often asked React interview questions:
1- What is React? Why Is It Necessary?
When designing user interfaces for apps with a single page, React is a handy front-end JavaScript library. Because it follows a component-based approach, it is useful for creating sophisticated and reusable UI components for mobile and online apps. We use React, which has all the power of JavaScript but with built-in capabilities that help us design and think about constructing apps more efficiently.
- It facilitates the usage of technologies like JSX for the creation of user interfaces.
- In contrast to static HTML, it allows us to quickly exchange components of our user interface
(UI). - With React hooks, we can develop reusable functionality across all of our components.
- Instead of having to manually update the DOM whenever our data changes, React does this for
us.
2- What are React’s drawbacks?
The following are a few of React’s drawbacks:
- Because it is only a library, React cannot be considered a framework in the traditional sense.
- It will take some time to get familiar with all of React’s components.
- Beginner programmers may have a hard time understanding React.
- Inline templating and JSX may make coding more difficult.
3- What is the difference between ReactJS and Angular?
| ReactJS | Angular |
|---|---|
| It uses javascript & JSX | It uses javascript & HTML |
| Its allows 1-way data binding | Its allows 2-way data binding |
| Its uses Virtual DOM | It Uses Real DOM |
| It’s faster than Angular | It’s slower than ReactJS |
4- Virtual DOM: What is it? What was the reason for the implementation of virtual DOM?
The React team has explained that virtual DOM is a notion where a virtual version of the actual DOM is preserved in memory and is synchronized with the real DOM via a library like ReactDOM.
Although JavaScript’s DOM manipulation is essential to web applications, it takes a long time to do it. When many DOM operations are taking place, the application’s performance suffers. It’s very uncommon for JavaScript frameworks to propagate changes to the whole DOM, even if they’re minor
For example, think of a list that is being displayed in the DOM as an example. Instead of merely rerendering the item that was altered or updated, the full list is re-rendered. Inefficient updating is the term for this. The react team came up with the notion of virtual DOM to solve the issue of inefficient updating.
5- Redux thunks are used for what?
To construct action creators that return functions instead of actions, Redux thunk operates as a middleware. The delay function may also be used to postpone the execution of action until a certain condition is fulfilled. As input to the inner function, the two store methods getState() and dispatch() are supplied.
First, we need to utilize the applyMiddleware() function as seen below:
import{ createStore, applyMiddleware } from 'redux';
import thunk from 'redux-thunk';
import rootReducer from './reducers/index';
const store= createStore(
rootReducer,
applyMiddleware(thunk)
);
6- What are React’s most important features?
First, let’s take a closer look at what makes React JS so popular. To further understand how React JS works, we’ll use this example.
i. React Native.
Native React JS development for Android and iOS is made easier with the use of native components rather than web components.
By integrating native functionalities into React code, this feature makes React code mobile-friendly for devices running iOS or Android.
ii. JavaScript XML (or JSX)
The app’s user interface is described using this markup format. Developers use it to generate React components because it mimics HTML syntax. One of the finest aspects of React JS is JSX, which simplifies the writing of the building blocks for developers.
iii. A ‘virtual DOM’
React’s quickness and adaptability are two of its most appealing features. React’s virtual memory may now hold a copy of a website, thanks to this approach. A virtual DOM is created to represent the actual DOM. The whole UI is re-rendered by the virtual DOM whenever the app is updated or modified, by updating the components that have been changed. As a result, development time and costs are cut.
iv. Data Binding in One Direction
Developers must utilize the callback functionality instead of directly altering components in React because of this unidirectional flow of data.
As part of the Flux app architectural component, a single point of control over data flow is established. In reality, it gives developers greater control over the program and allows it to be more adaptable and more effective.
v. Declarative UIs
Because of this functionality, it’s much simpler to debug and maintain React code. React JS is the greatest framework for creating new and engaging user interfaces for both online and mobile applications.
vi. Component-based design
An app built using React JS has a complex user interface that includes several JS-coded components, each of which has its unique logic. As a result, developers can move data across the app without affecting the DOM. A large portion of the app’s graphics and interactions are determined by React JS components.
7- What does React’s useState() do?
It’s possible to have state variables in functional components thanks to the useState() React Hook. For dynamically manipulating/controlling the DOM, it is appropriate to utilize this method.
UseState(0) will return a tuple with count as the first argument and setCounter method as the second parameter, which will enable us to adjust the counter’s current state in the provided example code.
..
const [count, setCounter] = useState(0);
const [otherStuffs, setOtherStuffs] = useState(..);
..
const setCount = () => {
setCounter(count + 1);
setOtherStuffs(..);
..
};
The setCounter() function may be used to update the count in any location. SetCounter() is used inside the setCount method in this example, where numerous other things may be done. Hooks allow us to make our code more functional and prevent the use of class-based components if they aren’t necessary.
8- Is there any use for the useEffect hook?
It is used to produce side effects in functional components using the useEffect React Hook To tell React that your component needs something to be done after it has been rendered or after a state change, you may use useEffect to do so. As soon as the DOM update performance is complete, React will remember and run the function you gave (also known as “effect”). Calculations such as obtaining data, altering the page title, and modifying the DOM directly may all be done with this method. By default, the useEffect hook is activated after the initial render and every change to the component. The DOM will be updated by the time the effect has finished running.
React Hook useEffect may take two arguments: useEffect(callback[, dependencies]);
The function with side-effect logic is represented by the first parameter callback, which is run immediately after modifications are pushed to the DOM. The dependencies array in the second parameter may be whatever you want it to be. As long as dependencies change between renderings, useEffect() will be called.
import { useEffect } from 'react';
function WelcomeGreetings({ name }) {
const msg = `Hi, ${name}!`;
useEffect(() => {
document.title = `Welcome to you ${name}`;
}, [name]);
return <div>{msg}</div>;
}
Because the preceding code does not directly compute the component output, it is called a side-effect. As a result, useEffect has been given a callback that performs document title updates ().
Is there any chance that if you don’t want to do a document title update on the WelcomeGreetings component’s rendering every time, you’ll need to provide a name as a dependency for useEffect(callback, [name]).
9- In React, what is the Flux Concept?
The flux architecture idea is often used by Facebook to construct client-side web apps. Not a framework or library, it’s just a bunch of code. Just a new sort of architecture to go along with React and the Unidirectional Data Flow notion.
10- Describe a few ways to make a React app run faster.
Let’s have a look at some of how one might improve the speed of a React app:
i. Invoking the function useMemo()
- CPU-intensive functions may be cached using this React hook.
- Re-rendering a component in a React app might cause a CPU-Expensive function to be run repeatedly, resulting in delayed rendering. Such routines may be cached using the useMemo() hook. UseMemo() ensures that the CPU-intensive function is only used when it is really necessary.
ii. Using PureComponent – React.Pure
- To determine whether or not a component should be changed, this class examines the component’s state and properties.
- We may use React. Component instead of the plain React.Component. To limit the number of re-renders of a component, PureComponent has been implemented.
iii. Keeping the State Cooperative
- The goal is to get the state as near as possible to where you want it.
- Many superfluous states may be found in the parent component of React apps, making it more difficult to comprehend and maintain the code. As a side note, having many states in a single component causes the component to re-render itself.
- States that aren’t as important to the parent component should be moved to a separate one.
Wrapping Up
I hope this list of Top 10 React Interview Questions will help you in preparing for your interviews. All the best!
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