Litmus7 Systems Consulting Reactjs Developer Interview Questions and Answers

A reducer is a pure function in React that takes the previous state and an action, and returns the new state.

• Reducers are used in React to manage state changes in an application

• They take the previous state and an action as input

• Reducers are pure functions, meaning they do not modify the state directly

• They return a new state based on the previous state and the action

• Redux is a popular library that uses reducers to manag

New features of HTML5 and CSS positions include flexbox, grid layout, and sticky positioning.

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

• Grid layout enables the creation of complex layouts with rows and columns.

• Sticky positioning allows elements to stick to a specific position on the page as the user scrolls.

Spread operator is used to expand an iterable object into individual elements.

• Used for passing props to child components

• Used for merging arrays and objects

• Syntax: ...

• Example: const arr = [1, 2, 3]; const newArr = [...arr, 4, 5];

Hoisting is a JavaScript mechanism where variables and function declarations are moved to the top of their scope.

• Variables declared with var are hoisted to the top of their scope

• Function declarations are hoisted before variables

• Function expressions are not hoisted

• Hoisting can lead to unexpected behavior and bugs

useEffect is a hook in React that allows you to perform side effects in functional components.

• It replaces componentDidMount, componentDidUpdate, and componentWillUnmount.

• It takes two arguments: a function that performs the side effect and an array of dependencies.

• The function is called after every render, unless the dependencies haven't changed.

• Common use cases include fetching data, setting up event listeners, and upd...read more

Function currying is a technique of transforming a function that takes multiple arguments into a sequence of functions that each take a single argument.

• Currying allows partial application of a function.

• It helps in creating reusable functions.

• Curried functions are composable and can be easily combined to create new functions.

• Currying can be achieved using closures or by using libraries like Lodash or Ramda.

• Example: cons

Closures are functions that have access to variables in their outer scope, even after the outer function has returned.

• Closures are created when a function is defined inside another function.

• The inner function has access to the outer function's variables and parameters.

• Closures can be used to create private variables and methods.

• Closures can also be used to create functions with pre-set arguments.

React 16 introduced new features like React Fiber, Error Boundaries, Portals, and improved server-side rendering.

• React Fiber is a new reconciliation engine that improves performance and enables incremental rendering.

• Error Boundaries allow developers to catch and handle errors in components.

• Portals provide a way to render children into a different DOM subtree.

• Improved server-side rendering with support for streaming and...read more

React hooks simplify state management and lifecycle methods in functional components.

• Hooks allow functional components to have state and lifecycle methods

• They reduce the need for class components and HOCs

• Hooks make code more readable and easier to test

• Examples of hooks include useState, useEffect, and useContext

HOC components are higher-order components in React that allow code reuse and logic sharing.

• HOC components are functions that take a component and return a new component with additional functionality.

• They are used to abstract common logic and behaviors into reusable components.

• HOC components can be used for tasks like authentication, logging, and code reuse.

• Example: a withAuth HOC component that adds authentication log