How do you create a functional component in React?

To create a functional component in React, you simply define a JavaScript function that returns JSX .

1. Import React (not always necessary, but required if using JSX):

import React from 'react';

2. Define your functional component:

function MyFunctionalComponent() {
return (
// JSX code representing the component's UI
<div>
<h1>Hello, World!</h1>
</div>
);
}

3. Export your component:

export default MyFunctionalComponent;

Top React Components Interview Questions & Answers

React Component is the building blocks of the React application. It is the core concept that everyone must know while working on React. In this tutorial, we will see the top React Components questions that can be asked in the interview.

Let’s discuss some common questions that you should prepare for the interviews. These questions will be helpful in clearing the interviews, especially for the frontend development or full stack development role.

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1. What is a React component?

A Component is one of the core building blocks of React. In other words, we can say that every application you will develop in React will be made up of pieces called components. Components make the task of building UIs much easier. You can see a UI broken down into multiple individual pieces called components and work on them independently and merge them all in a parent component which will be your final UI....

2. What are the two types of React components?

The two types of React components are class components and functional components....

3. Differentiate between class component and functional component.

Feature Class Component Functional Component Syntax Extends React.Component class Simple JavaScript function State Can manage state using this.state and setState() Traditionally stateless, but can manage state using Hooks (useState) Lifecycle Methods Has access to lifecycle methods like componentDidMount() and componentDidUpdate() Does not have access to lifecycle methods (prior to Hooks) Boilerplate Typically requires more code and boilerplate Requires less code and is more concise Readability Can sometimes be more verbose and complex Generally more straightforward and readable...

4. How do you create a class component in React?

To create a class component in React, you typically define a JavaScript class that extends the React.Component class....

5. How do you create a functional component in React?

To create a functional component in React, you simply define a JavaScript function that returns JSX ....

6. What is the purpose of the render() method in a class component?

The render() method in a class component is a fundamental part of React’s component lifecycle. Its purpose is to define what should be rendered to the DOM when the component is rendered or updated....

7. How do you render a React component on the DOM?

To render a React component on the DOM, you typically use the ReactDOM.render() method....

8. What is JSX? How does it differ from HTML?

JSX stands for JavaScript XML. It is a syntax extension for JavaScript, often used with React to describe what the UI should look like. JSX may remind you of a template language, but it comes with the full power of JavaScript....

9. How can you pass props to a React component?

You can pass props to a React component by adding attributes to the component when you use it in JSX....

10. How do you access props inside a functional component?

To access props inside a functional component, you simply define the function with a parameter representing the props object. Then, you can access individual props from this object....

11. How do you access props inside a class component?

To access props inside a class component, you can use this.props within any method or lifecycle hook of the class....

12. What is state in React?

The state in React is an instance of the React Component Class that can be defined as an object of a set of observable properties that control the behavior of the component. In other words, the State of a component is an object that holds some information that may change over the lifetime of the component....

13. How state is different from props?

PROPS STATE The Data is passed from one component to another. The Data is passed within the component only. It is Immutable (cannot be modified). It is Mutable ( can be modified). Props can be used with state and functional components. The state can be used only with the state components/class component (Before 16.0). Props are read-only. The state is both read and write....

14. How do you initialize state in a class component?

In a class component in React, you initialize state in the constructor method....

15. How do you update state in React?

...

16. What is the purpose of the setState() method?

In React, you update state using the setState() method....

17. What are lifecycle methods in React?

...

18. Explain the lifecycle phases of a class component.

The setState() method in React is used to update the state of a component, triggering a re-render with the updated state. It manages state changes asynchronously that allows React to batch multiple updates for performance optimization. When calling setState(), React merges the provided state updates with the current state, updating only the specified properties....

19. What is the purpose of the componentDidMount() method?

Every React Component has a lifecycle of its own, lifecycle of a component can be defined as the series of methods that are invoked in different stages of the component’s existence. A React Component can go through four stages....

20. How do you fetch data from an API inside a React component?

Class Component can go through stages of its life as follows....

21. What is the purpose of the componentWillUnmount() method?

Purpose of componentDidMount lifecycle method...

22. How do you handle events in React?

To fetch data from an API inside a React component, you typically use the fetch() API or a library like Axios....

23. How do you conditionally render elements in React?

Purpose of the componentWillUnmount() method:...

24. What is the purpose of the && operator in JSX?

In React, you handle events using JSX by passing event handler functions as props to React elements....

25. How do you use the ternary operator for conditional rendering in React?

In React, you can conditionally render elements by using JavaScript expressions inside JSX....

26. What is a key prop in React?

The purpose of the && operator in JSX is to conditionally render elements based on a boolean expression. It allows you to render an element only if the expression evaluates to true, and if it evaluates to false, it will not render anything....

27. How do you render a list of items in React?

In React, you can use the ternary operator (condition ? trueValue : falseValue) for conditional rendering. This allows you to render different JSX elements based on a condition....

28. What is the purpose of the map() function in React?

The key prop in React is a special attribute used to uniquely identify elements within a collection (such as an array) when rendering lists of elements. It provides efficient updates to the UI by helping React determine which items have changed, been added, or been removed from the list. Keys should be unique among siblings and stable between renders, and they are essential for optimizing rendering performance and enabling efficient reconciliation of list updates....

29. What is component composition in React?

In React, you can render a list of items by mapping over an array of data and returning JSX elements for each item....

30. How do you compose multiple components together in React?

In React, the map() function is used for transforming arrays of data into arrays of JSX elements, and provides dynamic rendering of lists or collections of items in components. By iterating over each item in an array, map() allows you to perform operations on data, generate unique keys for efficient list rendering, and construct JSX elements based on data....

31. What are higher-order components (HOCs) in React?

Component composition in React is used for building complex user interfaces by combining smaller, reusable components together. This helps breaking down the UI into smaller, more manageable pieces, each responsible for specific functionality or UI elements. By combining these components hierarchically and passing data and behavior through props, you can create scalable, maintainable, and customizable UIs....

32. What are error boundaries in React?

In React, you compose multiple components together by nesting them within each other’s JSX. This hierarchical composition allows you to build complex user interfaces by combining smaller, reusable components into larger ones....

33. What is the purpose of the componentDidCatch() method?

...

34. How do you handle errors in a React component?

Higher-order components or HOC is the advanced method of reusing the component functionality logic. It simply takes the original component and returns the enhanced component....

35. What are some ways to optimize the performance of React components?

Error boundaries are a React component that catches JavaScript errors anywhere in their child component tree, log those errors, and display a fallback UI instead of crashing the entire component tree. They are used to ensure that errors in one part of the UI don’t affect the rest of the application....

36. What is memoization in React?

Purpose and usage of the componentDidCatch() method:...

37. What is code-splitting in React?

In React, you can handle errors in a component using the componentDidCatch() lifecycle method....

38. What are the different ways to style React components?

...