Top 10 ReactJS Questions

Discover the top essential questions for a ReactJS interview, curated to help hiring managers evaluate expertise and candidates to prepare thoroughly for their next role. Some samples about general questions about reactjs

1. What is React?
   • React is an open-source JavaScript library for building user interfaces. It allows developers to create reusable UI components and manage the state and props of an application efficiently.
2. How is React different from Angular or Vue?
   • React is primarily a library for building UIs, while Angular is a full-fledged MVC framework. Vue is a progressive framework but is more similar to React in terms of its focus on the view layer. Each has its own ecosystem, methodologies, and learning curves.
3. What is JSX?
   • JSX (JavaScript XML) is a syntax extension for JavaScript recommended by React. It looks like HTML in your JavaScript code and gets transcompiled by tools like Babel to pure JavaScript. It helps in describing the UI structure in a declarative way.
4. Can you explain the difference between state and props in React?
   • Props (short for “properties”) are a way of passing data from parent to child components. They are read-only. The state, on the other hand, is specific to a component and can change over time. It represents data that the component may change during its lifetime.
5. What are React hooks?
   • React hooks are functions that let developers “hook into” React state and lifecycle methods from function components. Commonly used hooks include useState, useEffect, and useContext.
6. What is the virtual DOM and how does it work in React?
   • The virtual DOM is an in-memory representation of the real DOM. When changes are made to the web page, React creates a virtual DOM to compare with the current one and updates only the changed parts in the real DOM. This diffing and patching process makes React efficient.
7. How do you handle events in React?
   • Events in React are handled with camelCase, and you pass them explicitly as callbacks. For instance, in HTML you might use onclick, but in React you’d use onClick.
8. What are controlled and uncontrolled components in React?
   • A controlled component has its value controlled by the state. Inputs in such components always display values from the component’s state and updates via functions. An uncontrolled component, on the other hand, maintains its own internal state – refs are typically used to get their values.
9. Can you explain the importance of keys in React?
   • Keys are used by React to identify which items in a list have changed, are added, or are removed. They should be given to the elements inside the array to give them a stable identity.
10. How does React handle form input?

• React treats form inputs as controlled components by default. That means the value of the input is controlled by the state of the component, and any updates to the input value should be saved back to the state using event handlers.

Remember, the depth and complexity of the answers can vary based on who is asking and in what context. The provided answers are concise and meant for a general overview.