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1.How do you check if a string starts with a specific substring in JavaScript?

str.beginsWith('substring')

str.startsWith('substring')

str.indexOf('substring') === 0

str.startsWithSubstring('substring')

2.What is the purpose of the `Object.getOwnPropertyNames()` method in JavaScript?

Returns an array of a given object's own enumerable property names

Returns an array of a given object's own enumerable and non-enumerable property names

Returns an array of a given object's own and inherited property names

Returns an array of a given object's values

3.How do you round a number to the nearest integer in JavaScript?

Math.ceil(x)

Math.floor(x)

Math.round(x)

round(x)

4.What does the following code log to the console?

console.log(typeof NaN);

NaN

string

number

undefined

5.How do you check if an object has a specific property in JavaScript?

if (myObj.property !== undefined)

if (myObj.hasProperty('property'))

if ('property' in myObj)

if (myObj.hasOwnProperty('property'))

6.What is the purpose of the `String.trim()` method in JavaScript?

Adds whitespace to both ends of a string

Removes whitespace from both ends of a string

Trims characters from the middle of a string

Converts a string to uppercase

7.What will be the output of the code?

console.log(3 > 2 > 1);

TRUE

FALSE

null

undefined

8.How do you convert a string to a date object with a specific format in JavaScript?

new Date('YYYY-MM-DD')

Use a library like Moment.js

Date.parse('YYYY-MM-DD')

new Date(str)

9.What is the purpose of the `String.lastIndexOf()` method in JavaScript?

Returns the length of the calling string

Replaces a specified substring with another substring

Returns a boolean indicating whether the calling string contains the specified value

Returns the index within the calling string of the last occurrence of the specified value

10.What is the output of the following code?

console.log([] == ![]);

null

FALSE

TRUE

undefined

11.How do you convert a string to a boolean in JavaScript?

str.convertToBoolean()

str.toBoolean()

Boolean(str)

if (str) { /* code */ }

12.What does the `Object.isFrozen()` method return in JavaScript?

`null`

The frozen object

A boolean indicating whether an object is frozen

`undefined`

13.What is the output of the following code?

console.log(0.1 + 0.2 === 0.3);

TRUE

FALSE

null

undefined

14.What is the purpose of the `Object.isSealed()` method in JavaScript?

Unseals an object, allowing modifications

Seals the object, preventing new properties from being added and existing properties from being deleted

Prevents an object from being modified

Returns a boolean indicating whether an object is sealed

15.How do you convert a string with commas to an array of substrings in JavaScript?

str.toSubstringsArray(',')

str.toArray()

Array.from(str, ',')

str.split(',')

16.What is the output of the following code?

console.log(null == undefined);

null

FALSE

TRUE

undefined

17.What is the purpose of the `String.slice()` method in JavaScript?

Adds characters to the end of a string

Removes the last character from a string

Returns a shallow copy of a portion of a string into a new string

Returns a shallow copy of a portion of an array into a new array

18.What is the purpose of the `Date.toDateString()` method in JavaScript?

Returns a string representing the date portion of the Date object

Returns the current date and time in the local time zone

Returns the number of milliseconds since January 1, 1970, 00:00:00 UTC

Converts a date to a string in the specified format

19.How do you declare a variable with a dynamic type in JavaScript?

let x = 42;

var x;

const x = 42;

var x = 42;

20.What will be the value of `x` after the code execution?

var x = 5; x += '3';

8

53

NaN

Error

General JS VI