20 React Context API Interview Questions and Answers

React Context API is a powerful tool that allows developers to manage state and data in React applications. When applying for a position that uses React, it is likely that employers will want to know if you are familiar with Context API and how to use it. Knowing how to answer common questions about Context API can help you impress the hiring manager and improve your chances of getting the job. In this article, we discuss the most common React Context API questions and how you should answer them.

React Context API Interview Questions and Answers

Here are 20 commonly asked React Context API interview questions and answers to prepare you for your interview:

1. What are the main features of React Context?

The main features of React Context are its ability to provide a way to pass data through the component tree without having to pass props down manually at every level, and its ability to provide a default value for a context if one is not provided by a parent component.

2. Can you explain what contexts are in the context of React?

Contexts in React provide a way to pass data through the component tree without having to explicitly pass props at every level. In other words, context allows you to share data that can be used by multiple components without having to explicitly pass it as props. Context is often used for things like managing the current authenticated user, theme, or locale.

3. How is the new API different from the old one?

The new API is different from the old one in a few key ways. First, the new API is more flexible and easier to use. It also allows for more than one context to be used in a single application. Finally, the new API is more efficient and will improve performance in applications that make use of it.

4. What’s the difference between using React Context and Redux for state management?

React Context is a way to pass data down the component tree without having to pass props manually at every level. This can be helpful if you have data that you need to be available to many components in your application. Redux is a state management library that can be used with React (or any other front-end framework). It helps to keep your application state organized and easy to update.

5. Can you give me some examples where it would be better to use a context than global variables or props?

Context can be really useful when you need to provide data that can be accessed by many components in your application. For example, if you need to provide a user’s authentication status or theme preference throughout your app, using context would be a good way to do that. Context can also be helpful when you need to pass data down through many levels of components, and you don’t want to have to pass props down manually at every level.

6. When should I use React Context API instead of Redux or MobX?

React Context API should be used when you need to share data throughout your app that is not specific to any one component. For example, if you need to provide a user authentication status or a theme to multiple components, React Context API would be a good solution. If you need to manage more complex state, then you would likely be better off using Redux or MobX.

7. What issues does the React Context API solve?

The React Context API solves the issue of prop drilling. Prop drilling is when a component needs data that is located several levels up in the component hierarchy. In order to get that data, the component has to pass the data down through all of the intermediate levels until it finally reaches the component that needs it. This can be a very tedious and error-prone process. The React Context API provides a way for components to access data that is located anywhere in the component hierarchy without having to pass the data down through all of the intermediate levels.

8. Is there a performance advantage to using the React Context API over other state management solutions like Redux, Flux, etc.?

While the React Context API does offer a performance advantage over other state management solutions, it is important to note that this advantage is only present when the application is re-rendering. When an application is first being loaded, the React Context API does not offer any performance benefits.

9. Can you explain how the Provider/Consumer pattern works with the React Context API?

The Provider/Consumer pattern is used to provide a way for React components to access the React Context API. The Provider component is used to provide the React Context API to the React components that are descendants of the Provider. The Consumer component is used to access the React Context API that is provided by the Provider.

10. Where can I find more information about the React Context API?

The React Context API is a relatively new feature, and as such there isn’t a ton of information out there about it yet. However, the React team has put together a good overview of the API on the React website, which can be found here: https://reactjs.org/docs/context.html. Additionally, there are a few good articles and tutorials out there that can help you get started with using the Context API in your own projects.

11. What are some guidelines for when to use this API?

The React Context API should be used when you need to pass data down the component tree without having to explicitly pass props at every level. This is especially useful when you have data that is used by many components, but only needs to be fetched once. It can also be helpful for managing state that is difficult to pass down props, such as state that depends on the window size or the current URL.

12. What do you understand about the legacy context API?

The legacy context API was a way for React components to access data that was provided by a parent component. This data could be anything, but was often used to provide theme information or other global data that needed to be accessed by many different components. The legacy context API has been deprecated in favor of the new context API, which is more flexible and easier to use.

13. Why was the legacy API removed?

The legacy API was removed in order to make the Context API simpler and more predictable. The new API is easier to use and understand, and it will help improve the performance of React applications.

14. How many consumers can be connected to a single provider?

There is no limit to the number of consumers that can be connected to a single provider.

15. How is react-redux-provider different from react-redux-connector?

React-redux-provider is a higher-order component that provides the store to all of its child components. React-redux-connector is a function that connects a React component to a Redux store.

16. What are the various ways by which a component can access data stored in context?

The various ways by which a component can access data stored in context are:

1. By using the static contextType property on the class.
2. By using the Consumer component.
3. By using the useContext Hook.

17. What problems can arise if an application uses too many providers?

The main problem that can arise from using too many providers is that the application can become slow and bloated. This is because each provider requires its own set of data, which can take up a lot of space and processing power. In addition, if providers are not used correctly, they can actually end up conflicting with each other and causing problems.

18. What happens if I declare multiple components that need access to the same context?

If you declare multiple components that need access to the same context, the context will be updated every time one of the components calls setContext. This means that all of the components will receive the updated context, regardless of whether they actually need it.

19. What are the differences between lifecycle methods provided by React Class & Functional Components?

React Class Components offer more lifecycle methods than Functional Components. React Class Components can have a constructor, while Functional Components cannot. React Class Components can have a render method, while Functional Components cannot. React Class Components can have a componentDidMount method, while Functional Components cannot. React Class Components can have a shouldComponentUpdate method, while Functional Components cannot. React Class Components can have a componentDidUpdate method, while Functional Components cannot. React Class Components can have a componentWillUnmount method, while Functional Components cannot.

20. What is the best way to avoid problems related to context updates (like infinite loops)?

The best way to avoid problems related to context updates is to make sure that you only update the context when absolutely necessary. This means only updating the context when the underlying data changes, and not unnecessarily re-rendering the component tree. If you do need to update the context, make sure to use the shouldComponentUpdate lifecycle method to optimize performance.