Virtusa Consulting Services React Js Frontend Developer Interview Questions and Answers

Promises in JavaScript are objects representing the eventual completion or failure of an asynchronous operation.

• Promises can be in one of three states: pending, fulfilled, or rejected.

• Promises can be chained using .then() to handle success and .catch() to handle errors.

• Promises can be created using the Promise constructor or by using async/await syntax.

useState is used to manage state in functional components, while useEffect is used to perform side effects in functional components.

• useState is used to declare state variables in functional components.

• useEffect is used to perform side effects in functional components, such as data fetching, subscriptions, or manually changing the DOM.

• useState does not trigger re-renders, while useEffect can be used to trigger re-render...read more

Callback hell is a situation where multiple nested callbacks make the code difficult to read and maintain.

• Occurs when multiple asynchronous operations are nested within each other

• Leads to deeply nested code structure which is hard to understand

• Can be avoided by using Promises, async/await, or modularizing code

Traditional functions are defined using the function keyword, while arrow functions are defined using a concise syntax with =>.

• Traditional functions are hoisted, while arrow functions are not.

• Arrow functions do not have their own 'this' keyword, they inherit it from the parent scope.

• Arrow functions are more concise and easier to read compared to traditional functions.

• Traditional functions are better for methods in obje...read more

Creating a counter in React to increment and decrement a value.

• Create a state variable to store the count value

• Use setState to update the count value

• Render the count value in the component

• Add buttons to increment and decrement the count value

Program to find frequency of letters in a string

• Create an object to store the frequency of each letter

• Loop through the string and increment the count of each letter in the object

• Convert the object into an array of strings with letter and frequency pairs

Iterate through the given string to check if the substring is present.

• Iterate through the given string and check if each character matches the first character of the substring.

• If a match is found, check the subsequent characters to see if they form the substring.

• Return true if the entire substring is found within the given string, otherwise return false.