Preparing for a Frontend Developer interview? Here are the most frequently asked React.js questions that you must know.

1. What is the difference between Real DOM and Virtual DOM?

The Real DOM is slow because every time something changes, it updates the entire tree structure. The Virtual DOM is a lightweight copy of the Real DOM. React uses it to verify what exactly changed and updates only that specific part (Reconciliation).

2. What are React Hooks?

Hooks are functions that let you "hook into" React state and lifecycle features from functional components. Before Hooks, we could only use state in Class Components.

Common Hooks:

• useState - For managing state.
• useEffect - For side effects (API calls, timers).
• useContext - For avoiding prop drilling.

3. What is the difference between State and Props?

State is internal data managed by the component itself (can be changed).
Props (Properties) are data passed from a parent component to a child component (cannot be changed by the child).

// Example of Props
const Welcome = (props) => {
  return 
Hello, {props.name}
;
};
            

4. What is Prop Drilling and how to avoid it?

Prop drilling happens when you pass data from a Parent component to a deep Child component through many intermediate components that don't need the data.

Solution: Use Context API or state management libraries like Redux to share data globally.

Want more questions? Check out the Node.js Interview Guide in the sidebar.