Senior React JS Developer Interview Questions and Answers

Singleton pattern ensures a class has only one instance and provides a global point of access to it.

• Used to control access to a shared resource such as a database connection or a logger instance

• Implemented by creating a class with a method that creates a new instance only if one doesn't exist, and returns the existing instance if it does

• Commonly used in React applications for managing global state with Redux or Context API

Strategy pattern is a behavioral design pattern that allows selecting an algorithm at runtime.

• Used strategy pattern in a shopping cart application to dynamically apply different discount strategies based on user type (e.g. regular customer, premium customer)

• Implemented strategy pattern in a payment processing system to handle different payment methods (e.g. credit card, PayPal, Apple Pay)

• Utilized strategy pattern in a traffic management system to dynamically switch between di...read more

SCSS provides benefits such as variables, nesting, mixins, and inheritance for more efficient and maintainable CSS code.

• Variables allow for easy reuse of values throughout stylesheets.

• Nesting helps to organize CSS rules in a more intuitive way.

• Mixins enable the reuse of styles across different elements.

• Inheritance allows styles to be inherited from one selector to another.

• SCSS can help improve code readability and maintainability.

Virtual DOM is a lightweight copy of the actual DOM in React, used for efficient updates.

• Virtual DOM is a concept where a lightweight copy of the actual DOM is created in memory.

• React uses the virtual DOM to efficiently update the actual DOM when there are changes in the application state.

• By comparing the virtual DOM with the actual DOM, React determines the minimal number of changes needed to update the UI.

• This helps in improving performance by reducing the number of DOM man...read more

Use context api to fetch api data in React

• Create a context to store the api data

• Use useContext hook to access the context in components

• Use useEffect hook to fetch data from api and update the context

• Pass the context provider to wrap the components that need the api data

Flexbox is a layout model in CSS used for creating flexible and responsive layouts.

• Flexbox allows for easy alignment and distribution of items within a container.

• It provides a more efficient way to design complex layouts compared to traditional CSS methods.

• Flexbox properties include justify-content, align-items, flex-direction, and flex-wrap.

Redux is a predictable state container for JavaScript apps.

• Redux stores the entire state of the application in a single immutable state tree.

• State is read-only and can only be changed by emitting an action, which describes what happened.

• Reducers specify how the application's state changes in response to actions.

• Redux uses pure functions to calculate the next state based on the previous state and the action.

• Components can subscribe to the Redux store to receive updates when th...read more

React Redux is a predictable state container for JavaScript apps.

• React Redux is a library that helps manage the state of a React application.

• It provides a centralized store for state management.

• Actions are dispatched to update the state, and components can subscribe to changes in the state.

• It helps in maintaining a single source of truth for the state of the application.