reactjsWhat are some common ReactJS interview questions?

1. What is ReactJS?

ReactJS is an open-source JavaScript library for building user interfaces. It is maintained by Facebook and a community of individual developers and companies. ReactJS allows developers to create large web applications that use data and can change over time without reloading the page.

2. What are the advantages of using ReactJS?

The main advantages of using ReactJS are its virtual DOM, component-based architecture, and its use of a one-way data flow. The virtual DOM allows ReactJS to update only the necessary parts of the page instead of reloading the entire page. Its component-based architecture allows developers to easily create reusable components. Lastly, its one-way data flow makes it easier to debug and maintain applications.

3. What is JSX?

JSX is a JavaScript syntax extension that allows developers to write HTML-like syntax in their ReactJS components. It makes it easier to read and write React components as it looks more like HTML than JavaScript.

const element = <h1>Hello, world!</h1>;
ReactDOM.render(element, document.getElementById('root'));

Output example

Hello, world!

4. What is the difference between a Class Component and a Functional Component?

Class Components are JavaScript classes that extend the React.Component class and have access to state and lifecycle methods. Functional Components are just JavaScript functions that accept props and return React elements. Class Components are used when state or lifecycle methods are needed, while Functional Components are used when only props are needed.

5. What is the difference between createElement and cloneElement?

createElement is used to create React elements, while cloneElement is used to clone existing elements and modify them. createElement takes the element type, props, and children as arguments and returns a React element. cloneElement takes an element, props, and children as arguments and returns a new React element with the original element’s props and children.

6. What is the purpose of using keys in ReactJS?

Keys are used to identify unique elements in a list. They help React identify which items have changed, are added, or are removed. This allows React to optimize the rendering of components when the list is updated.

7. What is the purpose of using refs in ReactJS?

Refs are used to access DOM nodes or React elements created in the render method. They allow developers to interact with the DOM without using state or lifecycle methods. Refs are also used when creating references to elements that need to be accessed outside of the render method.

Edit this code on GitHub