Interview Questions and Answers

let and const are block-scoped, while var is function-scoped. const is used for constants and cannot be reassigned.

Example:

const PI = 3.14; let x = 10; var y = 5;

Destructuring assignment allows you to extract values from arrays or objects and assign them to variables.

Example:

const person = { name: 'John', age: 30 }; const { name, age } = person;

The spread operator (...) is used to spread elements of an array or object, while the rest operator is used to collect elements into an array.

Example:

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

Promises are used for asynchronous programming. They represent a value that may be available now, or in the future, or never.

Example:

const fetchData = new Promise((resolve, reject) => { /* async operation */ });

Async/await is a syntax sugar for working with promises. It makes asynchronous code look and behave more like synchronous code.

Example:

async function fetchData() { const result = await fetch('https://example.com'); }

Modules allow you to split your code into multiple files. You can export and import functionality between modules.

Example:

export const PI = 3.14; import { PI } from './math';

The 'reduce' function is used to accumulate the elements of an array into a single value.

Example:

const numbers = [1, 2, 3, 4, 5]; const sum = numbers.reduce((acc, num) => acc + num, 0);

Symbols are a new primitive data type in ES6, used to create unique identifiers.

Example:

const mySymbol = Symbol('description');

A Set is a collection of values with no duplicate entries. It is iterable and can store various types of values.

Example:

const uniqueNumbers = new Set([1, 2, 3, 2, 1]);

Array.findIndex() is used to find the index of the first element in an array that satisfies a given condition.

Example:

const numbers = [1, 2, 3, 4, 5]; const index = numbers.findIndex(num => num > 2);