ES6 Interview Questions and Answers
Freshers / Beginner level questions & answers
Ques 1. What is the let keyword used for in ES6?
The let keyword is used to declare block-scoped variables.
Example:
let x = 10; if (true) { let x = 20; console.log(x); } console.log(x);
Ques 2. What are template literals in ES6?
Template literals are a way to create strings with embedded expressions. They are enclosed by backticks (`).
Example:
let name = 'John'; let greeting = `Hello, ${name}!`;
Ques 3. Explain the arrow functions in ES6.
Arrow functions are a concise way to write functions. They do not have their own 'this' and 'arguments'.
Example:
const add = (a, b) => a + b;
Ques 4. What is the purpose of the 'class' keyword in ES6?
The 'class' keyword is used to create classes in JavaScript for object-oriented programming.
Example:
class Person { constructor(name) { this.name = name; } }
Ques 5. What is the purpose of the 'map' function in ES6?
The 'map' function is used to transform each element of an array and create a new array with the results.
Example:
const numbers = [1, 2, 3]; const doubled = numbers.map(num => num * 2);
Ques 6. Explain the 'filter' function in ES6.
The 'filter' function is used to create a new array with elements that satisfy a given condition.
Example:
const numbers = [1, 2, 3, 4, 5]; const evens = numbers.filter(num => num % 2 === 0);
Ques 7. Explain the 'find' function in ES6.
The 'find' function is used to find the first element in an array that satisfies a given condition.
Example:
const numbers = [1, 2, 3, 4, 5]; const result = numbers.find(num => num > 2);
Ques 8. What are the rest parameters in ES6?
Rest parameters allow a function to accept an indefinite number of arguments as an array.
Example:
function sum(...numbers) { return numbers.reduce((acc, num) => acc + num, 0); }
Ques 9. What is the 'default parameter value' feature in ES6?
Default parameter values allow you to specify default values for function parameters if no value or undefined is passed.
Example:
function greet(name = 'Guest') { console.log(`Hello, ${name}!`); }
Ques 10. Explain the 'Object.assign()' method in ES6.
Object.assign() is used to copy the values of all enumerable own properties from one or more source objects to a target object.
Example:
const target = {}; const source = { a: 1, b: 2 }; Object.assign(target, source);
Ques 11. What is the 'Array.from()' method in ES6?
Array.from() is used to create a new shallow-copied array from an array-like or iterable object.
Example:
const arrayLike = { 0: 'a', 1: 'b', length: 2 }; const newArray = Array.from(arrayLike);
Ques 12. Explain the 'Array.of()' method in ES6.
Array.of() is used to create a new array with a variable number of arguments, regardless of their types.
Example:
const newArray = Array.of(1, 'hello', true);
Ques 13. Explain the 'Array.includes()' method in ES6.
Array.includes() is used to check if an array includes a certain element, returning true or false.
Example:
const numbers = [1, 2, 3, 4, 5]; const includesThree = numbers.includes(3);
Ques 14. What is the 'Object.entries()' method in ES6?
Object.entries() is used to return an array of a given object's own enumerable string-keyed property [key, value] pairs.
Example:
const obj = { a: 1, b: 2 }; const entries = Object.entries(obj);
Ques 15. Explain the 'Object.keys()' method in ES6.
Object.keys() is used to return an array of a given object's own enumerable string-keyed property names.
Example:
const obj = { a: 1, b: 2 }; const keys = Object.keys(obj);
Ques 16. What is the purpose of the 'Object.values()' method in ES6?
Object.values() is used to return an array of a given object's own enumerable string-keyed property values.
Example:
const obj = { a: 1, b: 2 }; const values = Object.values(obj);
Ques 17. Explain the concept of the 'for...of' loop in ES6.
The 'for...of' loop is used to iterate over values in an iterable object, such as an array, string, or Map.
Example:
const arr = [1, 2, 3]; for (const num of arr) { console.log(num); }
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