Introduction
If you want to stand out in ReactJS interviews and grow your career, you should learn the fundamentals of React as it is still the most popular front-end programming framework. Here you can get answers to some of the most common and difficult interview questions regarding React JS that hiring managers are anticipated to ask.
Whether you’re training for a senior-level position for the first time or just want to brush up on your skills, these React JS interview questions can help you show off your knowledge of the framework and get the job you want.
Why Is A React JS Developer A Popular Job Role?
The many useful features and functions provided by the React JS library are a big reason why this skill set is so popular. Companies are increasingly using it because of its scalability, simplicity of use in designing dynamic user interfaces, and flexibility, which in turn increases the demand for qualified workers. Among the many benefits of React JS are its component-based design, virtual DOM for rendering, short learning curve, and large community support.
In addition, the library offers a large ecosystem, programming that is friendly to search engines, quick rendering, and code that is reusable and easy to maintain.
To enhance your skill set in the fast-paced world of technology, continuous learning is essential. Alongside mastering ReactJS, consider exploring other in-demand areas such as data science, machine learning, and cloud computing. A free data science course can provide valuable insights into data handling, analysis, and visualization techniques. This knowledge can set you apart in job interviews and help you adapt to the evolving tech landscape, making you a more versatile candidate for a variety of roles within the industry.
React Interview Questions & Answers
1. What is React?
React is an open-source JavaScript library for the front end that facilitates the creation of user interfaces for single-page applications. Due to its component-based design, it is useful for developing sophisticated and reusable UI components for online and mobile apps.
2. Why should you use React? What benefits does it offer?
- Boosting performance using Virtual DOM: To display the view, React employs virtual DOM. A virtual DOM is an abstract version of the actual document object model (DOM), as the name implies. In a react app, a new virtual document object (DOM) is produced whenever the data changes. Instead of generating the user interface in the browser, a virtual DOM can be quickly created. Consequently, the app’s efficiency is enhanced with the use of virtual DOM.
- Ease of learning: In contrast to frameworks like as Angular, React’s learning curve is rather flat. One can begin the development of web apps with React, even with limited knowledge of JavaScript.
- SEO friendly: With React, programmers can create interactive user interfaces that are compatible with all major search engines. It also enables server-side rendering, which is great for an app’s search engine optimization.
- Reusable components: Application development using React is facilitated by its component-based design. Code that is both separate and reusable is called a component. Applications with comparable features can make use of these components. The rate of development is accelerated by reusing components.
An extensive network of libraries to pick from: You can personalize the tools, frameworks, and architecture you use to build an app with React to your specific needs.
3. What are the limitations of React?
Here are the few boundaries to be considered while using React:
- Since it is only a library, React does not constitute a complete framework.
- It will take some time to have a good grasp of all of React’s components because there are so many.
- Beginners of computer programming may find React challenging.
- Using inline templating and JSX could make the code more complicated.
4. In React, what does useState() mean?
With the help of the useState() hook, which is pre-installed in React, you may incorporate state variables into your functional components. When the DOM has an element that may be controlled or modified dynamically, this method should be employed.
The count is the first parameter in the useState(0) function, which returns a tuple representing the current state of the counter. The second parameter, setCounter, allows us to alter the state of the counter, as seen in the following sample 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 status globally. Inside the setCount method, where a lot of other things may be done, you may use setCounter() as shown in the example. By utilizing hooks, you may keep your code more useful and eliminate unnecessary class-based components.
5. What is the virtual DOM?
The term “virtual DOM” refers to an approach wherein a library, like ReactDOM, maintains an in-memory representation of the actual DOM and synchronizes it with the real DOM.
6. How come virtual DOM was created?
Even though it’s essential to any online project, DOM manipulation is incredibly sluggish compared to other JavaScript activities. When several DOM operations are being performed, the application’s efficiency is compromised. To accommodate even minor DOM changes, the majority of JavaScript frameworks update the complete document object model (DOM).
Just think of a list being rendered inside the DOM as an example. When an item in the list is edited, the whole list is re-rendered rather than only the modified or updated item. It’s called “inefficient updating.” The react team came up with the idea of virtual DOM to fix the issue of slow updating.
7. How is Virtual DOM implemented?
There is a virtual DOM object (copy) that corresponds to each DOM object and shares all of its characteristics. The fundamental difference among a real DOM object and a virtual DOM object is that the second kind does not instantaneously reflect changes in the first one’s visual representation on the screen. A virtual DOM object is like a scale model of its physical counterpart. All virtual DOM objects are updated whenever a JSX element is displayed.
React employs two virtual DOMs throughout the process of rendering of the UI. The objects’ present state is saved in one of them, while their past state is stored in the other. Whenever there is an update to the virtual DOM, react checks both versions to see which objects were changed. Rather than rendering the entire actual DOM, react renders only the items that were modified once it knows which ones. React mitigates the problem of sluggish updates by employing a virtual DOM.
8. Why are browsers unable to interpret JSX?
Although browsers are capable of reading JavaScript objects, JSX is not one of those objects. To enable a browser to interpret JSX, it is necessary to utilize JSX transformers like Babel to turn the JSX file into a JavaScript object, which can then be sent to the browser.
9. React recognizes that everything can be a component. Give an example.
The user interface (UI) of a React app is constructed using components. The complete user interface is broken down into smaller, more manageable, and reusable parts by these components. After that, it creates separate UI elements that don’t interact with one another.
10. Describe the function render() and its function in React.
A render() method is required for every React component. It takes the native DOM component and returns one React element that represents it. A single enclosing tag, such as <form>, <group>,<div> etc., is required for the rendering of several HTML elements. This function has to be pure, meaning it needs to always return the same thing.
11. How may several components be integrated into a single one?
The below procedure can be employed to combine components into a singular entity:
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | class MyComponent extends React.Component{ render(){ return( <div> <h1>Hello</h1> <Header/> </div> ); } } class Header extends React.Component{ render(){ return <h1>Header Component</h1> }; } ReactDOM.render( <MyComponent/>, document.getElementById(‘content’) ); |
12. What is Props?
By “props,” we mean “properties” in the React language. These components are read-only and must remain unchanged. They are consistently transmitted from the parent component to the child components inside the application. Props may solely be transported from a parent component to a child component. Not vice versa. Typically used to display data that is created dynamically, they aid in preserving the one-way data flow.
13. Clarify the notion of state and its use in React
At their core, React components are states. Data comes from states, thus it’s important to keep them as basic as feasible. To put it simply, states are the objects that control how components look and act. In contrast to the props, they may be changed to make new parts that are both dynamic and interactive. They are accessed via this.state().
14. Define the various types of side effects that can occur in a React component.
Two kinds of unintended consequences might occur while using a React component. Here they are:
- Effects without Cleanup: The useEffect method, which does not prevent the browser from updating the screen, will make use of this side effect. Furthermore, it enhances an application’s efficiency. Examples include logging, network queries, manual DOM changes, and so forth.
- Effects with Cleanup: Following DOM updates, cleaning may be necessary for some Hook effects. For instance, clearing the RAM is necessary before configuring an external data source subscription; otherwise, a memory leak might occur. It is well-known that when components are unmounted, React will clear up the memory. However, instead of running for a single function, the effects will be applied to all render() methods. So, it’s safe to claim that React will clean away the effects from the previous render before executing them the next time.
15. What is the optimal method for managing browser resizing and re-rendering?
In componentDidMount(), you can watch for the resize event and modify the height and width as needed. In the componentWillUnmount() method, you must remove the event listener for it to work.
When the browser’s size changes, we may display the view using the code shown below:
class WindowSizeDimensions extends React.Component {
constructor(props){
super(props);
this.updateDimension = this.updateDimension.bind(this);
}
componentWillMount() {
this.updateDimension()
}
componentDidMount() {
window.addEventListener(‘resize’, this.updateDimension)
}
componentWillUnmount() {
window.removeEventListener(‘resize’, this.updateDimension)
}
updateDimension() {
this.setState({width: window.innerWidth, height: window.innerHeight})
}
render() {
return <span>{this.state.width} x {this.state.height}</span>
}
}
16. What is React’s one-way data binding?
Component-to-View and View-to-Component data binding are both supported in ReactJS. The term “one-way data flow” describes the situation when information may only go in one direction within an application. This basically prevents child components from making changes to the data that is being sent from the parent component. It has a low mistake rate and is simple to troubleshoot.
Conclusion
The world’s leading IT firms, particularly those based in India, are increasingly using React. This includes Facebook, PayPal, Instagram, Uber, and many more. Hooks are quickly gaining popularity in the React community due to the fact that they simplify state management.
To assist you in being prepared for your interview, this post contains the most commonly asked questions and answers on and around ReactJS. Keep in mind that your conduct and the first impact you create will have just as much of an impact on your interview outcome as your technical abilities. Best of luck!
