JavaScript Test your knowledge Quiz
Question 1: What is the primary purpose of the this keyword in JavaScript?
A) To refer to the previous line of code
B) To reference the current object or context
C) To access the parent element in the DOM
D) To declare a new variable
Answer: B) To reference the current object or context
Question 2: Which built-in JavaScript method is used to remove the last element from an array?
A) splice()
B) slice()
C) shift()
D) pop()
Answer: D) pop()
Question 3: How do you declare a constant variable in JavaScript?
A) let
B) var
C) const
D) constant
Answer: C) const
Question 4: What is the purpose of the map() function in JavaScript?
A) To create a new array with the results of calling a provided function on every element in the array
B) To remove elements from an array
C) To concatenate two arrays
D) To sort an array in ascending order
Answer: A) To create a new array with the results of calling a provided function on every element in the array
Question 5: Which operator is used to combine two or more conditions in an if statement in JavaScript?
A) and
B) &
C) &&
D) ||
Answer: C) &&
Question 6: What is the purpose of the break statement in JavaScript?
A) To exit a loop or switch statement prematurely
B) To skip the current iteration of a loop
C) To continue to the next iteration of a loop
D) To define a new function
Answer: A) To exit a loop or switch statement prematurely
Question 7: What is the result of the expression 2 + “2” in JavaScript?
A) 22
B) 4
C) 2 + 2
D) TypeError
Answer: A) 22
Question 8: What is the purpose of the parseInt() function in JavaScript?
A) To convert a string to a floating-point number
B) To convert a floating-point number to a string
C) To convert a string to an integer
D) To convert an integer to a string
Answer: C) To convert a string to an integer
Question 9: What is the JavaScript operator for checking if two values are not equal, regardless of their data types?
A) !=
B) !==
C) =/=
D) ==
Answer: B) !==
Question 10: Which JavaScript function is used to find the index of the first occurrence of a specified value in an array?
A) find()
B) indexOf()
C) search()
D) contains()
Answer: B) indexOf()
Question 11: What is the purpose of the typeof operator in JavaScript?
A) To check if a variable is undefined
B) To check the type of a value or variable
C) To convert a value to a different type
D) To check if a variable is null
Answer: B) To check the type of a value or variable
Question 12: How do you declare a multiline string in JavaScript?
A) Enclose the string in double quotes
B) Use the backslash character at the end of each line
C) Enclose the string in single quotes
D) Use template literals with backticks
Answer: D) Use template literals with backticks
Question 13: What does the querySelector() method do in JavaScript?
A) Selects the first element that matches a specified CSS selector
B) Adds an event listener to an element
C) Changes the background color of the page
D) Removes an element from the DOM
Answer: A) Selects the first element that matches a specified CSS selector
Question 14: What is the purpose of the localStorage object in JavaScript?
A) To store session data on the server
B) To store data in the client’s browser
C) To make AJAX requests
D) To create a new JavaScript file
Answer: B) To store data in the client’s browser
Question 15: How can you add a comment in your JavaScript code that won’t be executed?
A) // This is a comment
B) <!– This is a comment –>
C) /** This is a comment **/
D) # This is a comment #
Answer: A) // This is a comment
Question 16: What is the result of typeof null in JavaScript?
A) “undefined”
B) “object”
C) “null”
D) “string”
Answer: B) “object”
Question 17: Which JavaScript function is used to add elements to the end of an array?
A) push()
B) append()
C) add()
D) concat()
Answer: A) push()
Question 18: What is the purpose of the try…catch statement in JavaScript?
A) To define a new function
B) To declare a variable
C) To handle exceptions and errors
D) To create a loop
Answer: C) To handle exceptions and errors
Question 19: Which method is used to convert an object to a JSON string in JavaScript?
A) objectToString()
B) toJSON()
C) JSON.stringify()
D) stringifyObject()
Answer: C) JSON.stringify()
Question 20: What does the Math.floor() function do in JavaScript?
A) Rounds a number up to the nearest integer
B) Rounds a number down to the nearest integer
C) Returns the absolute value of a number
D) Computes the square root of a number
Answer: B) Rounds a number down to the nearest integer
Question 21: Which JavaScript function is used to remove the first element from an array?
A) shift()
B) removeFirst()
C) splice()
D) delete()
Answer: A) shift()
Question 22: What is the purpose of the event.preventDefault() method in JavaScript?
A) To execute the default action for an event
B) To stop the event from propagating to parent elements
C) To prevent the default behavior of an event
D) To trigger an event
Answer: C) To prevent the default behavior of an event
Question 23: What is the result of the expression “5” – 2 in JavaScript?
A) 7
B) “52”
C) 3
D) NaN
Answer: C) 3
Question 24: How can you check the length of an array in JavaScript?
A) Using the length() method
B) Using the count property
C) Using the size() method
D) Using the length property
Answer: D) Using the length property