Cognizant Interview Questions and Answers

display none removes element from layout, visibility hidden hides element but still takes up space

• display none removes element from layout flow

• visibility hidden hides element but still takes up space

• display none is more efficient for hiding elements

• visibility hidden is better for hiding elements while keeping layout intact

Spread operator is used to split up array elements or object properties, while rest operator is used to merge multiple elements into an array.

• Spread operator is denoted by three dots (...) and is used to spread array elements or object properties.

• Rest operator is also denoted by three dots (...) and is used to collect multiple elements into a single array.

• Spread operator can be used to concatenate arrays or objects, while rest operator can be used to gather function arguments...read more

React virtual DOM is a lightweight copy of the actual DOM, used for efficient updates and rendering in React applications.

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

• React compares the virtual DOM with the actual DOM and only updates the necessary parts for better performance.

• This helps in minimizing the number of DOM manipulations and improves the overall performance of React applications.

ES6 features are new additions to JavaScript introduced in ECMAScript 2015.

• Arrow functions for more concise syntax: const add = (a, b) => a + b;

• Let and const for block-scoped variables: let x = 5; const y = 10;

• Template literals for easier string interpolation: const name = 'John'; console.log(`Hello, ${name}!`);

• Classes for object-oriented programming: class Person { constructor(name) { this.name = name; } }

• Destructuring assignment for easily extracting values from objects or ...read more

A high order function is a function that takes one or more functions as arguments or returns a function as its result.

• High order functions can be used to create more flexible and reusable code.

• They can be used to abstract and encapsulate common patterns in code.

• Examples include map, filter, and reduce functions in JavaScript.

var is function scoped, let is block scoped, const is block scoped and cannot be reassigned.

• var is function scoped

• let is block scoped

• const is block scoped and cannot be reassigned

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

• Variable declarations are hoisted to the top of their scope but not their initializations.

• Function declarations are fully hoisted, including their definitions.

• Hoisting can lead to unexpected behavior if not understood properly.