If you are looking for a job in the React field, then you will need to be prepared for some tough questions. In this blog post, we will list the top 15 questions that are likely to be asked in an interview in 2022. We will also provide tips on how to answer these questions effectively. So whether you are just starting out in your React career or you are looking to switch jobs, this blog post is for you!
1. What is React? Why Use It as a developer?
React refers to a JavaScript library that is used in creating user interfaces. It allows you to create reusable components to organize and easily maintain your code. React is popular because it delivers fast and smooth web pages. In addition, React is growing in popularity because it works well with other JavaScript libraries such as Redux and AngularJS.
There are many reasons to use React, but some of the key benefits include:
- React is used by major companies such as Facebook, Instagram, Netflix, and Airbnb.
- It is a popular choice for web development because it makes creating dynamic and responsive user interfaces simple.
- In addition, React code is easy to read and understand, which makes it a good choice for developers who are just starting out.
- Fast and smooth web pages
- Reusable components
- Works well with other JavaScript libraries
2. What are the features of React?
Some of its key features include:
- React is declarative, which means that you can create simple and readable code by describing what should be done rather than how it should be done.
- React is efficient, meaning that it updates only the parts of the DOM that have changed, which results in faster page load times.
- React is flexible, meaning that it can be used for both small and large projects.
3. How do you pass data to React components?
There are two ways to pass data to React components: props and state.
Props are immutable, meaning that the component cannot change them. They are passed down from the parent component to the child component. State, on the other hand, is mutable. The component can also access its own state and the state of its parent component.
When deciding which method to use, you need to consider how the data will be used. If the data is going to be changed by the component, then you should use state. If the data is only going to be used once and doesn’t need to be updated, you should use props.
In order to pass data from one component to another, you need to use the “props” and “state” keywords.
For example:
componentA.prop = “some value”;
componentB.state = { someValue: componentA.prop };
The above code will pass the “some value” from componentA to componentB. ComponentB can then access this value by using the “this.state.someValue” keyword.
4. What are the main advantages of React?
The main advantages of React are its speed and flexibility. React is able to render quickly, even on mobile devices. And because it is a library rather than a framework, React can be flexibly integrated into existing projects.
React also has a large community of developers who always create new libraries and tools that make working with React even easier. For example, React Native allows you to create mobile apps with React.
5. What are the limitations of React?
One of the limitations of React is that it does not support two-way data binding. This means that if you want to update the state of a component, you will need to use a callback function. Additionally, React only supports one-way data flow. This can be seen as a limitation because it can make code more difficult to reason about.
However, there are several workarounds for these limitations. For example, you can use a library like Redux to manage your state or use React Router to create nested components. Additionally, the development community is constantly coming up with new solutions to problems, so these limitations will likely be addressed in future versions of React.
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6. What is the difference between props and state?
This is a question that is commonly asked in React interviews. Props are immutable and should be used for data that will not change, such as the name of a user. On the other hand, state is mutable and can be used for data that will change, such as the user’s current location.
When it comes to choosing between props and state, it is important to remember that props are passed down from a parent component, while any component in the tree can change state. So if you want to update the state of a child component, you will need to use the this.setState() function.
Here is an example of how you would use props and state in a React component:
“`
class UserProfile extends React.Component {
constructor(props) {
super(props);
this.state = {
name: props.name,
location: “New York”
7. What is JSX?
JSX is a syntax extension to JavaScript. It was created to make writing React components easier. With JSX, you can write your component’s markup and logic in the same file.
This makes it simpler to reason about your code and keeps your project more organized. JSX is not required to use React, but it makes writing React code a lot more enjoyable.
8. Why can’t browsers read JSX?
JSX is a preprocessor that takes JS code and turns it into regular JavaScript. This means that browsers can’t read JSX files because they are not in the correct format. However, when your React application is running, JSX gets converted back into regular JavaScript, which browsers can understand.
Tip: When answering this question, be sure to mention that JSX is a preprocessor that helps make writing React code easier. You should also explain how JSX gets converted back into regular JavaScript when your application is running.
9. What are React Fragments used for?
React fragments are used to create reusable components. They allow you to split up a component into multiple elements, which can then be rendered separately. This is useful for building components containing multiple HTML chunks, such as a header and footer.
10. When should you use refs in React?
Refs should be used when you need to access the DOM directly. For example, if you need to modify an element’s CSS or innerHTML, then you will need to use a ref.
Tip: If possible, try to avoid using refs and instead use state and props. Refs should be adopted as a last resort only.
11. What is Redux, and what are its components?
Redux refers to a library that is used for managing state in React applications. It helps you keep your application’s state in a single place, making it easier to manage and debug.
There are three main components in Redux:
- Action: This is a class that represents an action that has been dispatched.
- Reducer: This is a function that takes action and a state and returns a new state.
- Store: This is a class that manages the state of your application. It contains the reducer and the current state.
12. Differentiate React and React Native
React is a JavaScript library for building user interfaces, while React Native is a framework that allows you to create native apps for mobile devices. React is used for web development, while React Native can be used for mobile app development. Both technologies are created by Facebook.
13. What are the differences between React and other popular front-end frameworks?
React differs from other popular front-end frameworks, such as Angular and Vue, in that it focuses on simplicity and speed. React also has a strong community behind it, which means there are always new updates and resources being created.
14. What is your experience with Redux?
Redux is popular because it allows you to manage large amounts of data easily. I have used Redux in many of my own projects, and I found it to be a very powerful tool.
15. What is your experience with React Router?
React Router is a popular library for creating single-page applications in React. It allows you to define routes and components, making it easy to create complex applications. I have used React Router in a few of my own projects, and I found it to be a very useful tool.
16. What are the pros and cons of React?
There are many pros and cons to React. Some of the pros include that it is easy to learn, fast, and can be used for both web and mobile development. Some of the cons include that there can be a steep learning curve, and it is not as widely adopted as other technologies.
17. What are the stages of the React component lifecycle?
The React component lifecycle can be divided into three distinct phases:
- Mounting
- Updating
- Unmounting
Each of these phases has its own purpose and methods that are invoked at different stages. For instance, in the mounting phase, the component is inserted into the DOM. This is when the `componentWillMount()` and `render()` methods are called. Meanwhile, in the updating phase, the component is updated in response to changes in props or state. This is when the `componentWillReceiveProps()`, `shouldComponentUpdate()`, and `componentWillUpdate()` methods are invoked. Finally, the component is removed from the DOM in the unmounting phase. This is when the `componentWillUnmount()` method is called.
Knowing which methods are invoked at each stage of the React component lifecycle is important for two reasons. First, it allows you to understand what is happening under the hood when a component is being rendered or updated. Second, it allows you to write more efficient and reliable code. For example, you can avoid calling it unnecessarily if you know that a method will only be invoked in the updating phase.
When it comes to React interviews, expect questions about the component lifecycle. Be prepared to answer questions such as:
- What are the different stages of the React component lifecycle?
- What is the purpose of each stage?
- What methods are invoked during each stage?
- How can you write code that is more efficient and reliable?
18. What is the useEffect hook used for?
The useEffect hook is used for side effects in React components. Side effects are operations that are not necessary for the component to render, but they can be performed before or after the component renders.
Examples of side effects include fetching data from a remote API, setting up a subscription, and changing the document title. The useEffect hook takes a function as an argument and runs that function after the component renders.
19. What is the purpose of render() in React.js?
The purpose of render() is to return a React element that will be displayed on the screen. This function takes in an argument called props, which contains information about the component. The rendered element can be used to calculate the final DOM structure.
20. What is hook in React?
Hooks are a new feature in React 16. Hoks allow you to use state as well as other React features without the need of writing a class.
Hooks are classified into: Effect Hooks and State Hooks.
- State Hooks allow you to create components that have local state. This is similar to the this.state property that you can use in a class component.
- Effect Hooks allow you to add side effects to your components. This is similar to the this.effect property that you can use in a class component.
21. What is the error boundary in React?
An error boundary is a React component that catches errors and displays them to the user. If an error occurs within a child component, the error boundary will catch it and display it to the user. This allows you to easily handle errors without having to worry about tracking down every individual component.
To create an error boundary, simply extend the Component class and add the errorBoundary prop. You will also need to implement the onError handler, which will be called when an error occurs.
22. What is the constructor in React?
The constructor in React is a function that is called when an object is created. It can be used to set up initial state for the object, or to perform any other initialization tasks.
An important thing to note about the constructor in React is that it does not have access to the DOM. This means that you cannot use it to manipulate the DOM directly. If you need to do any DOM manipulation, you will need to use a different function such as ReactDOM.render().
Tip: When answering questions about the constructor in React, always be sure to mention that it does not have access to the DOM. This will help to ensure that you are giving the correct answer.
Final Thoughts
The React field is growing rapidly, and the questions asked in interviews are getting more challenging. However, if you are prepared for these 15 questions, you will ace your interview and get the job you want.
However, keep in mind that the best way to ace an interview is to be well-prepared and confident. So practice answering these questions, and you will be sure to impress your interviewer! Good luck. Thanks for reading!
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