JavaScript Basics Questions and Answers

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#1. What is the correct syntax for referring to an external JavaScript file?

#2. Where is the correct place to insert JavaScript in an HTML document?

Inside the <head> tag

Inside the <body> tag

Outside of HTML tags

Both <head> and <body> tags

#3. How do you write a single-line comment in JavaScript?

# This is a comment

/* This is a comment */

// This is a comment

#4. Which keyword is used to declare a variable in JavaScript?

const

All of the above

var

let

#5. What is the output of console.log(typeof null)?

undefined

object

string

null

#6. How do you call a function named myFunction in JavaScript?

function myFunction();

myFunction();

execute myFunction();

call myFunction();

#7. What does NaN represent in JavaScript?

Not a Number

None of the above

Not a Name

Not a Null

#8. Which operator is used to compare both value and type in JavaScript?

!==

===

#9. How can you add a comment that spans multiple lines in JavaScript?

// Comment

/* Comment */

/* Comment -- */

#10. What is the default value of an uninitialized variable in JavaScript?

NaN

null

undefined

#11. What will the code console.log(“5” + 5) output?

Error

NaN

#12. What is the purpose of Array.isArray() method?

To create an array

To return the length of an array

To check if a variable is an array

To convert an object into an array

#13. What does the this keyword refer to in JavaScript?

None of the above

The parent function

The global object

The object that is currently executing the code

#14. Which function is used to parse a string to an integer in JavaScript?

String()

Number()

parseFloat()

parseInt()

#15. What is the result of 2 + “2” in JavaScript?

undefined

NaN

#16. How do you declare a constant in JavaScript?

const constantName = value;

constant constantName = value;

let constantName = value;

var constantName = value;

#17. What does == compare in JavaScript?

None of the above

Both value and type

Value

Type

#18. How do you create an array in JavaScript?

var arr = array("item1", "item2");

var arr = new Array("item1", "item2");

Both b and c

var arr = [“item1”, “item2”];

#19. What does the push() method do in an array?

Removes the last element of the array

Adds one or more elements to the end of the array

Removes the first element of the array

Adds one or more elements to the beginning of the array

#20. Which of the following is not a JavaScript framework?

React

Vue.js

Angular

Laravel

#21. What is the output of console.log(1 == “1”)?

false

true

Error

undefined

#22. What is the output of console.log(1 === “1”)?

Error

false

true

undefined

#23. How do you convert a string to a number in JavaScript?

Number("123")

+"123"

parseInt("123")

All of the above

#24. What does typeof [] return in JavaScript?

null

array

undefined

object

#25. Which method is used to remove the last element from an array?

push()

pop()

shift()

unshift()

#26. What is the purpose of the splice() method in JavaScript?

To add elements to an array

To replace elements in an array

To remove elements from an array

All of the above

#27. Which keyword is used to check for a specific condition in JavaScript?

else

switch

case

#28. What will the code console.log(typeof undefined) return?

undefined

null

string

object

#29. How can you get the length of a string in JavaScript?

string.size

string.length

string.count

string.len

#30. What is the output of console.log([] + {}) in JavaScript?

[object Object]

NaN

Error

[]

#31. What is the scope of a variable declared with let?

Both b and c

Global

Block

Function

#32. What will console.log(0.1 + 0.2 === 0.3) return?

true

false

undefined

Error

#33. How do you write an arrow function in JavaScript?

None of the above

const func = () => {}

=> function() {}

function => () {}

#34. Which method is used to join two or more arrays in JavaScript?

merge()

push()

join()

concat()

#35. How do you define a default parameter in JavaScript?

function example(a = 10) {}

function example(a == 10) {}

function example(a, 10) {}

function example(default a = 10) {}

#36. What is the difference between null and undefined in JavaScript?

null is an object, undefined is a type

Both are the same

None of the above

null represents an uninitialized variable, undefined means missing value

#37. How do you check if a value is NaN?

isNaN(value)

value == NaN

typeof value == "NaN"

value === NaN

#38. Which loop is guaranteed to execute at least once?

for

while

None of the above

do-while

#39. How do you create a new object in JavaScript?

Both b and c

let obj = {};

let obj = new Object();

let obj = Object();

#40. How do you access an object’s property using a variable?

object->variable

object.get(variable)

object.variable

object[variable]

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There are Multiple Choice Questions

Correct answers color: Green

Wrong answers color: Red

#1. What is the correct syntax for referring to an external JavaScript file?

#2. Where is the correct place to insert JavaScript in an HTML document?

#3. How do you write a single-line comment in JavaScript?

#4. Which keyword is used to declare a variable in JavaScript?

#5. What is the output of console.log(typeof null)?

#6. How do you call a function named myFunction in JavaScript?

#7. What does NaN represent in JavaScript?

#8. Which operator is used to compare both value and type in JavaScript?

#9. How can you add a comment that spans multiple lines in JavaScript?

#10. What is the default value of an uninitialized variable in JavaScript?

#11. What will the code console.log(“5” + 5) output?

#12. What is the purpose of Array.isArray() method?

#13. What does the this keyword refer to in JavaScript?

#14. Which function is used to parse a string to an integer in JavaScript?

#15. What is the result of 2 + “2” in JavaScript?

#16. How do you declare a constant in JavaScript?

#17. What does == compare in JavaScript?

#18. How do you create an array in JavaScript?

#19. What does the push() method do in an array?

#20. Which of the following is not a JavaScript framework?

#21. What is the output of console.log(1 == “1”)?

#22. What is the output of console.log(1 === “1”)?

#23. How do you convert a string to a number in JavaScript?

#24. What does typeof [] return in JavaScript?

#25. Which method is used to remove the last element from an array?

#26. What is the purpose of the splice() method in JavaScript?

#27. Which keyword is used to check for a specific condition in JavaScript?

#28. What will the code console.log(typeof undefined) return?

#29. How can you get the length of a string in JavaScript?

#30. What is the output of console.log([] + {}) in JavaScript?

#31. What is the scope of a variable declared with let?

#32. What will console.log(0.1 + 0.2 === 0.3) return?

#33. How do you write an arrow function in JavaScript?

#34. Which method is used to join two or more arrays in JavaScript?

#35. How do you define a default parameter in JavaScript?

#36. What is the difference between null and undefined in JavaScript?

#37. How do you check if a value is NaN?

#38. Which loop is guaranteed to execute at least once?

#39. How do you create a new object in JavaScript?

#40. How do you access an object’s property using a variable?

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