JavaScript Multiple Choice Questions (MCQs) and Answers

Q31 What is wrong with this function declaration?
function power(base, exponent) {
if (exponent == 0) return 1;
else return base * power(base, exponent - 1);
} console.log(power(2));

Q32 Which method is used to add an element to the end of an array in JavaScript?

Q33 How do you find the length of an array in JavaScript?

Q34 What does the splice method do in an array?

Q35 In JavaScript, how can you check if a variable is an array?

Q36 Which of the following array methods in JavaScript does not change the original array?

Q37 What is the output of this code snippet?
let arr = [10, 20, 30, 40];
let newArr = arr.map(x => x / 10);
console.log(newArr);

Q38 What is the output of the following code?
let fruits = ['apple', 'banana', 'mango'];
console.log(fruits[1]);

Q39 What will be the output of this code snippet?
let numbers = [1, 2, 3];
numbers[10] = 11;
console.log(numbers.length);

Q40 Consider the following code:
let arr = [1, 2, 3];
arr[5] = 5;
console.log(arr.filter(x => x === undefined).length);
What is the output?

Q41 Identify the issue in this array declaration:
let numbers = new Array(-5);

Q42 Spot the mistake in this code snippet:
let data = [1, 2, 3];
delete data[1];
console.log(data[1]);

Q43 How do you access the value of a property in a JavaScript object?

Q44 What will be the output of console.log(typeof {})?

Q45 In JavaScript, what is a method?

Q46 How do you create a new object in JavaScript?

Q47 What is the purpose of the this keyword in JavaScript objects?

Q48 What is the result of accessing a property that doesn’t exist on an object?

Q49 What is the output of the following code snippet?
let obj = { a: 1, b: 2 };
console.log(obj.a);

Q50 Consider the code:
let person = { name: 'Alice', age: 25 };
delete person.age; console.log(person.age);
What is the output?

Q51 Given the following code, what is printed to the console?
let obj1 = { a: 1 };
let obj2 = { a: 1 };
console.log(obj1 === obj2);

Q52 Find the issue in this object definition:
let obj = { '1a': 10, b: 20 };
console.log(obj.1a);

Q53 Identify the error in this object method:
let obj = {
greet: function() {
return 'Hello, ' + name;
}
};
console.log(obj.greet());

Q54 What does DOM stand for in web development?

Q55 Which JavaScript method is used to select an HTML element by its ID?

Q56 How can you change the text content of an HTML element in the DOM using JavaScript?

Q57 What is the difference between innerHTML and textContent properties in DOM manipulation?

Q58 What is the output of this code if the HTML contains an element with id demo and text 'Hello'?
document.getElementById('demo').textContent = 'Hi'; console.log(document.getElementById('demo').textContent);

Q59 Consider this code:
let items = document.querySelectorAll('.item');
console.log(items.length);
What does it output if there are three elements with class item in the HTML?

Q60 What will be the result of the following code if the HTML has multiple p tags?
let paragraphs = document.getElementsByTagName('p');
for(let i = 0; i < paragraphs.length; i++) {
paragraphs[i].style.color = 'blue';
}