In a technical interview focused on React.js, the interviewer would likely ask questions that touch upon various aspects of the library, its features, concepts, and best practices.

Here are 10 must know interview questions that you should know when interviewing for a job in React:

1. Explain the virtual DOM in React?

React's virtual DOM is an abstraction of the actual DOM. It's a lightweight copy of the actual DOM that React uses to understand what parts of the real DOM need to change when an event happens (like user interaction or data arrival).

2. What is JSX and how does it relate to React?

JSX is a syntax extension for JavaScript which is used to describe what the UI should look like. It is not necessary to use React but it's recommended due to its readability and simplicity.

3. What is the significance of keys in React?

Keys are used by React to identify individual elements. They're necessary when creating arrays of elements, as they help React optimize re-rendering by quickly identifying changes among siblings.

4. What are the lifecycle methods in a React Component?

Lifecycle methods control what happens from the time a component is created to when it is destroyed. As of React 16.3, there are different lifecycle methods, including constructor(), render(), componentDidMount(), shouldComponentUpdate(), getSnapshotBeforeUpdate(), componentDidUpdate(), and componentWillUnmount().

5. What are state and props in React?

State and props are ways that data gets handled in React. State is internal to a component and controls the behavior of the component from within. Props (short for properties) are external and control the component from outside.

6. What are functional components vs class components in React?

Functional components are simply JavaScript functions that return JSX. Class components are ES6 classes that extend from React.Component and have a render method.

7. What is Redux and how does it work with React?

Redux is a state management library. It helps manage global state in an application, beyond the state of individual components. It works well with React because it allows for predictable flow of data and more consistent behavior.

8. Can you describe how to implement forms in React?

Forms in React can be implemented using controlled or uncontrolled components. You'd typically use the state to control the inputs' values and define functions to handle changes and submission.

9. What are hooks in React?

Hooks are a new addition in React 16.8 that let you use state and other React features without writing a class. Examples are useState, useEffect, useContext, etc.

10. What is the context API in React?

The Context API is a way to share values between components without having to explicitly pass a prop through every level of the tree. Context is primarily used when some data needs to be accessible by many components at different nesting levels.

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