ES6+ Features Questions and Answers

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#1. Which keyword is block-scoped in JavaScript?

var and let

const

let and const

var

#2. What is the correct syntax for an arrow function?

function => {}

() -> {}

() => {}

=> {}

#3. Which of these is a correct example of destructuring assignment?

A). let {x, y} = [10, 20];

C). let {x, y} = {x: 10, y: 20};

D). Both B and C

B). let [x, y] = [10, 20];

#4. How do you declare a default parameter in a function?

None of the above

function test(a = 1) {}

function test(a: 1) {}

function test(a, default 1) {}

#5. What does the spread operator (…) do?

Expands elements of an array or object

All of the above

Combines arrays or objects

Copies arrays or objects

#6. What is a Promise in JavaScript?

A function for handling errors

A way to create callbacks

A data structure for arrays

An object representing the eventual completion of an asynchronous operation

#7. What method is used to check if an array includes a specific element?

indexOf()

has()

includes()

find()

#8. Which of the following methods is NOT available in ES6+?

Object.values()

Object.keys()

Object.entries()

Object.filter()

#9. What is the purpose of the for…of loop?

Iterates over iterable elements

Iterates over the length of an array

Iterates over object properties

Iterates over keys of an object

#10. How are modules imported in ES6?

A). require('module')

C) import module from 'module'

D) Both B and C

B) import 'module'

#11. What is the nullish coalescing operator (??) used for?

C) To create fallback values

B) To combine strings

D) Both A and C

A) To check if a value is null or undefined

#12. Which ES6+ feature allows iteration over the properties of an object?

forEach()

Object.entries()

for...of

for...in

#13. What is the output of const x = [1, 2, 3].map((n) => n * 2);?

[4, 6]

[2, 4, 6]

[2, 4]

[1, 2, 3]

#14. Which method is used to create a shallow copy of an object?

Object.assign()

Object.from()

Object.copy()

Object.clone()

#15. What is the significance of the super keyword in JavaScript classes?

Accesses child class methods

Refers to the parent class

Creates a new method

None of the above

#16. Which of the following is NOT an ES6+ data structure?

WeakMap

Map

Queue

Set

#17. What does the Array.flat() method do?

Converts an object into an array

Creates a deep copy of an array

Removes duplicates from an array

Merges nested arrays into a single array

#18. What is the default value of this in an arrow function?

The window object

The value of this from the surrounding context

The global object

Undefined

#19. Which of the following is a new type introduced in ES6+ for large integers?

LongInt

HugeInt

BigNum

BigInt

#20. What is the purpose of the at() method for arrays?

To sort the array

To get the last element of an array

To access elements at negative indices

To find the position of a specific element

#21. What is the purpose of the Object.fromEntries() method in ES6+?

Merge two objects

Delete object properties

Convert an array of key-value pairs into an object

Convert an object into an array of key-value pairs

#22. Which of the following allows for string interpolation in ES6+?

None of the above

Double quotes (")

Single quotes (')

Template literals (````)

#23. Which statement correctly uses a Set in ES6+?

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

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

const s = new Set(1, 2, 3);

const s = Set(1, 2, 3);

#24. What does the Array.find() method return?

The index of the first matching element

Undefined if no match is found

An array of all matching elements

The first element that satisfies the condition

#25. Which symbol is used for creating private fields in ES6+ classes?

#26. What does the Array.some() method do?

Both 2 and 3

Returns true if at least one element meets a condition

Returns true if all elements meet a condition

Returns false if no elements meet a condition

#27. What is the purpose of the Reflect API in ES6+?

To handle asynchronous operations

To manage promises

To simplify array manipulations

To provide methods for intercepting object operations

#28. What is a tagged template in JavaScript?

A template for defining HTML elements

A way to style strings

A template literal with a function to process it

A method for creating object keys

#29. How can you handle optional chaining in JavaScript?

Using ??.

Using ?

Using ?.

Using ??

#30. Which of these methods creates a new string by padding the original string?

String.extend()

String.pad()

String.fill()

String.padStart()

#31. What does Array.from() do?

Converts an array into an object

Merges multiple arrays into one

Fills an array with a specific value

Creates a new array from an iterable or array-like object

#32. What is the output of […’hello’] in ES6+?

[[‘h’], [‘e’], [‘l’], [‘l’], [‘o’]]

Throws an error

[‘h’, ‘e’, ‘l’, ‘l’, ‘o’]

[‘hello’]

#33. How do you export multiple variables in ES6+?

export(var1, var2);

export var1, var2;

export { var1, var2 };

export default var1, var2;

#34. What is the difference between Map and WeakMap?

WeakMap allows primitive keys

Both 1 and 2

WeakMap keys must be objects

Map does not have garbage collection

#35. What is the purpose of Array.prototype.flatMap()?

To create a copy of an array

To merge multiple arrays

To flatten nested arrays

To map and flatten arrays in one operation

#36. Which of these is a feature of ES6+ classes?

Private methods using #

All of the above

Static methods

Inheritance using extends

#37. What is the significance of the Symbol type in JavaScript?

All of the above

It defines hidden object properties

It allows primitive types to be iterable

It creates unique object keys

#38. What is the output of the following code? javascript Copy code const a = 10; console.log(a ?? 20);

undefined

Throws an error

#39. Which of these is a benefit of using default exports?

Allows multiple exports in one file

Makes functions private

Helps destructure the imported object

Simplifies importing modules

#40. What does Promise.all() do?

Resolves when all promises resolve

Rejects immediately if one promise rejects

Resolves with the first resolved promise

Both 1 and 3

Both 2 and 3

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ES6+ Features

There are Multiple Choice Questions

Correct answers color: Green

Wrong answers color: Red

#1. Which keyword is block-scoped in JavaScript?

#2. What is the correct syntax for an arrow function?

#3. Which of these is a correct example of destructuring assignment?

#4. How do you declare a default parameter in a function?

#5. What does the spread operator (…) do?

#6. What is a Promise in JavaScript?

#7. What method is used to check if an array includes a specific element?

#8. Which of the following methods is NOT available in ES6+?

#9. What is the purpose of the for…of loop?

#10. How are modules imported in ES6?

#11. What is the nullish coalescing operator (??) used for?

#12. Which ES6+ feature allows iteration over the properties of an object?

#13. What is the output of const x = [1, 2, 3].map((n) => n * 2);?

#14. Which method is used to create a shallow copy of an object?

#15. What is the significance of the super keyword in JavaScript classes?

#16. Which of the following is NOT an ES6+ data structure?

#17. What does the Array.flat() method do?

#18. What is the default value of this in an arrow function?

#19. Which of the following is a new type introduced in ES6+ for large integers?

#20. What is the purpose of the at() method for arrays?

#21. What is the purpose of the Object.fromEntries() method in ES6+?

#22. Which of the following allows for string interpolation in ES6+?

#23. Which statement correctly uses a Set in ES6+?

#24. What does the Array.find() method return?

#25. Which symbol is used for creating private fields in ES6+ classes?

#26. What does the Array.some() method do?

#27. What is the purpose of the Reflect API in ES6+?

#28. What is a tagged template in JavaScript?

#29. How can you handle optional chaining in JavaScript?

#30. Which of these methods creates a new string by padding the original string?

#31. What does Array.from() do?

#32. What is the output of […’hello’] in ES6+?

#33. How do you export multiple variables in ES6+?

#34. What is the difference between Map and WeakMap?

#35. What is the purpose of Array.prototype.flatMap()?

#36. Which of these is a feature of ES6+ classes?

#37. What is the significance of the Symbol type in JavaScript?

#38. What is the output of the following code? javascript Copy code const a = 10; console.log(a ?? 20);

#39. Which of these is a benefit of using default exports?

#40. What does Promise.all() do?

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