Cognizant Reactjs Developer Interview Questions and Answers

Closure is a feature in JavaScript that allows a function to access variables in its outer scope.

• A closure is created when a function is defined inside another function.

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

• The outer function's variables and parameters are not accessible from outside the closure.

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

• Example: function outer() { let x = 10; function inner() { console.log(x); } retu...read more

ES6 features are new additions to JavaScript language syntax and functionality.

• Arrow functions

• Template literals

• Let and const keywords

• Destructuring assignment

• Spread and rest operators

• Classes

• Modules

• Promises

• Default parameters

• Object.assign()

• Symbol data type

To reverse a string, iterate through the characters and swap them from start to end.

• Create an empty string to store the reversed result.

• Iterate through the characters of the input string from end to start.

• Append each character to the empty string to reverse the order.

• Return the reversed string.

Redux workflow involves actions, reducers, and store to manage application state.

• Actions are dispatched to describe what happened in the application

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

• Store holds the application state and allows access to it

• Components can subscribe to the store to receive updates when the state changes

Virtual DOM is a lightweight copy of the actual DOM that React uses to improve performance by minimizing actual DOM manipulations.

• Virtual DOM is a concept where a lightweight copy of the actual DOM is created and manipulated by React.

• React uses the virtual DOM to efficiently update the actual DOM by only making necessary changes.

• When state or props change in a React component, a new virtual DOM representation is created and compared with the previous one to determine the mini...read more

Counter application using Reactjs

• Create a React component for the counter

• Use state to keep track of the count

• Implement functions to increment and decrement the count

• Display the count on the screen

Splice is used to add/remove elements from an array, while slice is used to extract a portion of an array without modifying the original array.

• Splice modifies the original array, while slice does not.

• Splice can add elements, remove elements, or replace elements in an array.

• Slice returns a new array with the selected elements from the original array.

• Example: const arr = [1, 2, 3, 4, 5]; arr.splice(2, 1); // removes element at index 2, arr is now [1, 2, 4, 5]; const newArr = ar...read more