Sharpen Your JavaScript Skills with These Multiple-Choice Questions

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JavaScript Questions

Test your knowledge

1. What is JavaScript?

a) A programming language

b) A database management system

c) A markup language

d) An operating system

Answer: a) A programming language

2. What is the purpose of the "typeof" operator in JavaScript?

a) To check the data type of a variable

b) To create a new variable

c) To concatenate strings

d) To define a function

Answer: a) To check the data type of a variable

3. How do you declare a variable in JavaScript?

a) var

b) variable

c) v

d) let

Answer: a) var

4. What does the "===" operator in JavaScript do?

a) Compares values for equality without type coercion

b) Assigns a value to a variable

c) Checks if a variable is defined

d) Performs bitwise XOR operation

Answer: a) Compares values for equality without type coercion

5. What is the result of the expression "5 + '5'"?

a) 10

b) 55

c) 25

d) "55"

Answer: d) "55"

6. Which keyword is used to define a function in JavaScript?

a) function

b) def

c) func

d) define

Answer: a) function

7. What is the purpose of the "return" statement in a function?

a) To print a value to the console

b) To exit the function and return a value

c) To declare a variable

d) To concatenate strings

Answer: b) To exit the function and return a value

8. How do you comment a single-line in JavaScript?

a) //

b) /* */

c) #

d) ---

Answer: a) //

9. What is the difference between "null" and "undefined" in JavaScript?

a) They are the same

b) "null" represents the absence of a value, while "undefined" is a variable that has been declared but not assigned a value

c) "undefined" represents the absence of a value, while "null" is a variable that has been declared but not assigned a value

d) "null" and "undefined" are both used to represent an empty string

Answer: b) "null" represents the absence of a value, while "undefined" is a variable that has been declared but not assigned a value

10. What does the "this" keyword refer to in JavaScript?

a) The current function

b) The global object

c) The parent object

d) The variable being passed to a function

Answer: b) The global object

11. How do you check if a variable is an array in JavaScript?

a) isArray()

b) isObject()

c) typeofArray()

d) arrayCheck()

Answer: a) isArray()

12. What does the "map" function do in JavaScript?

a) Iterates over the elements of an array and applies a function to each element

b) Creates a new array with all elements that pass a test

c) Filters the elements of an array based on a condition

d) Reduces the array to a single value

Answer: a) Iterates over the elements of an array and applies a function to each element

13. Which keyword is used to prevent a variable from being modified?

a) freeze

b) const

c) lock

d) protect

Answer: b) const

14. What is a closure in JavaScript?

a) A way to close a function

b) A function inside another function that has access to the outer function's variables

c) A type of loop

d) A variable declared within a function

Answer: b) A function inside another function that has access to the outer function's variables

15. What is the purpose of the "setTimeout" function in JavaScript?

a) Delays the execution of a function by a specified number of milliseconds

b) Repeats the execution of a function at a set interval

c) Halts the execution of a function

d) Sets the time zone of the script

Answer: a) Delays the execution of a function by a specified number of milliseconds

16. What does the "JSON" acronym stand for in JavaScript?

a) JavaScript Object Notation

b) Java Syntax Object Notation

c) Just Simple Object Naming

d) JavaScript Oriented Notation

Answer: a) JavaScript Object Notation

17. How do you handle errors in JavaScript?

a) try-catch

b) error()

c) catch-throw

d) handle-error

Answer: a) try-catch

18. What does the "isNaN" function do?

a) Checks if a value is not a number

b) Checks if a value is a number

c) Converts a string to a number

d) Rounds a number to the nearest integer

Answer: a) Checks if a value is not a number

19. What is the purpose of the "push" method in JavaScript?

a) Adds elements to the end of an array

b) Removes elements from the beginning of an array

c) Adds elements to the beginning of an array

d) Removes elements from the end of an array

Answer: a) Adds elements to the end of an array

20. How do you create a new object in JavaScript?

a) new Object()

b) createObject()

c) {}

d) Object.create()

Answer: c) {}

21. What is the difference between "let," "const," and "var" for variable declaration?

a) They are interchangeable

b) "let" is block-scoped, "const" is block-scoped and cannot be reassigned, and "var" is function-scoped

c) "let" is block-scoped, "const" is function-scoped, and "var" is block-scoped

d) "let" is function-scoped, "const" is block-scoped, and "var" is function-scoped

Answer: b) "let" is block-scoped, "const" is block-scoped and cannot be reassigned, and "var" is function-scoped

22. What is the purpose of the "splice" method in JavaScript?

a) Removes elements from an array and returns the removed elements

b) Adds elements to an array and returns the new array length

c) Concatenates two arrays

d) Reverses the elements of an array

Answer: a) Removes elements from an array and returns the removed elements

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

a) parseInt()

b) toNumber()

c) Number()

d) stringToNumber()

Answer: c) Number()

24. What is the purpose of the "querySelector" method in JavaScript?

a) Selects the first element that matches a specified CSS selector

b) Selects all elements that match a specified CSS selector

c) Selects the last element that matches a specified CSS selector

d) Selects an element by its ID

Answer: a) Selects the first element that matches a specified CSS selector

25. What is the difference between "null" and "undefined"?

a) They are the same

b) "null" represents the absence of a value, while "undefined" is a variable that has been declared but not assigned a value

c) "undefined" represents the absence of a value, while "null" is a variable that has been declared but not assigned a value

d) "null" and "undefined" are both used to represent an empty string

Answer: b) "null" represents the absence of a value, while "undefined" is a variable that has been declared but not assigned a value

26. What does the "bind" method do in JavaScript?

a) Creates a new array with the results of calling a function for every array element

b) Binds a function to a particular object, ensuring that "this" refers to the specified object

c) Combines two arrays into one

d) Creates a copy of an array with the elements reversed

Answer: b) Binds a function to a particular object, ensuring that "this" refers to the specified object

27. What is an IIFE (Immediately Invoked Function Expression) in JavaScript?

a) A function that is automatically invoked when the script loads

b) A function that is executed only when called explicitly

c) A function that is defined inside another function

d) A function that runs forever

Answer: a) A function that is automatically invoked when the script loads

28. What is the purpose of the "Promise" object in JavaScript?

a) To handle asynchronous operations and represent a value that might be available now, or in the future, or never

b) To create a new object

c) To check if a variable is defined

d) To concatenate strings

Answer: a) To handle asynchronous operations and represent a value that might be available now, or in the future, or never

29. What is the purpose of the "filter" method in JavaScript?

a) Iterates over the elements of an array and applies a function to each element

b) Creates a new array with all elements that pass a test

c) Combines two arrays into one

d) Reduces the array to a single value

Answer: b) Creates a new array with all elements that pass a test

30. How do you declare a constant variable in JavaScript?

a) const

b) let

c) var

d) constant

Answer: a) const

31. What does the "addEventListener" method do in JavaScript?

a) Adds an event listener to a DOM element

b) Removes an event listener from a DOM element

c) Appends a new child element to a parent element

d) Adds a new event to the event queue

Answer: a) Adds an event listener to a DOM element

32. What is the purpose of the "charAt" method in JavaScript?

a) Returns the character at a specified index in a string

b) Concatenates two strings

c) Converts a string to uppercase

d) Returns the length of a string

Answer: a) Returns the character at a specified index in a string

33. How do you reverse the order of elements in an array?

a) reverse()

b) flip()

c) invert()

d) backward()

Answer: a) reverse()

34. What is the purpose of the "event.preventDefault()" method in JavaScript?

a) Stops the propagation of an event to parent elements

b) Prevents the default action associated with an event from occurring

c) Captures all events in the document

d) Removes an event listener from a DOM element

Answer: b) Prevents the default action associated with an event from occurring

35. What is the purpose of the "querySelectorAll" method in JavaScript?

a) Selects the first element that matches a specified CSS selector

b) Selects all elements that match a specified CSS selector

c) Selects the last element that matches a specified CSS selector

d) Selects an element by its ID

Answer: b) Selects all elements that match a specified CSS selector

36. What is the purpose of the "concat" method in JavaScript?

a) Combines two arrays into one

b) Creates a new array with the results of calling a function for every array element

c) Adds elements to the end of an array

d) Removes elements from an array

Answer: a) Combines two arrays into one

37. What is the output of the following code?

javascript

Copy code

console.log(1 + '1' - 1);

a) 10

b) 11

c) 01

d) "11"

Answer: b) 11

38. What is the purpose of the "slice" method in JavaScript?

a) Returns a section of a string

b) Removes elements from an array and returns the removed elements

c) Adds elements to the end of an array

d) Reverses the elements of an array

Answer: a) Returns a section of a string

39. What does the "toLowerCase" method do in JavaScript?

a) Converts a string to lowercase

b) Converts a string to uppercase

c) Removes leading and trailing whitespaces from a string

d) Splits a string into an array of substrings

Answer: a) Converts a string to lowercase

40. What is the purpose of the "shift" method in JavaScript?

a) Adds elements to the end of an array

b) Removes elements from the beginning of an array

c) Adds elements to the beginning of an array

d) Removes elements from the end of an array

Answer: b) Removes elements from the beginning of an array

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

a) toString()

b) toText()

c) stringify()

d) numberToString()

Answer: a) toString()

42. What is the purpose of the "find" method in JavaScript?

a) Iterates over the elements of an array and applies a function to each element

b) Creates a new array with all elements that pass a test

c) Returns the first element in an array that satisfies a provided testing function

d) Reduces the array to a single value

Answer: c) Returns the first element in an array that satisfies a provided testing function

43. What is the purpose of the "includes" method in JavaScript?

a) Checks if a value is not a number

b) Checks if a value is a number

c) Checks if an array includes a certain element

d) Checks if a string includes a certain substring

Answer: c) Checks if an array includes a certain element