JavaScript MCQ: JavaScript Multiple Choice Questions and Answers

JavaScript MCQ with answers and explanations for placement tests and job interviews. These solved JavaScript MCQ are useful for the campus placement for all freshers including Engineering Students, MCA students, Computer and IT Engineers, etc.

Our JavaScript MCQ ( JavaScript multiple Choice Questions ) focuses on all areas of JavaScript and its concept. We will regularly update the quiz and most interesting thing is that questions come in a random sequence. So every time you will feel new questions.

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Guideline of JavaScript MCQ:

This JavaScript MCQ is intended for checking your JavaScript knowledge. It takes 1 hour to pass the JavaScript MCQ. If you don’t finish the JavaScript MCQ within the mentioned time, all the unanswered questions will count as wrong. You can miss the questions by clicking the “Next” button and return to the previous questions by the “Previous” button. Every unanswered question will count as wrong. MCQ on JavaScript has features of randomization which feel you a new question set at every attempt.

In this JavaScript MCQ, we have also implemented a feature that not allowed the user to see the next question or finish the quiz without attempting the current JavaScript MCQ.

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Javascript MCQ

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Javascript MCQ: Javascript Multiple Choice Questions and Answers

1 / 82

Which method cancels event default behavior?

2 / 82

What value does this code return?
let answer = true;
if (answer === false) {
return 0;
} else {
return 10;
}

3 / 82

Which statement is used to skip iteration of the loop?

4 / 82

Which operator returns true if the two compared values are not equal?

5 / 82

What is the HTTP verb to request the contents of an existing resource?

6 / 82

What will this code print?
var v = 1;
var f1 = function () {
console.log(v);
};

var f2 = function () {
var v = 2;
f1();
};

f2();

7 / 82

For the following class, how do you get the value of 42 from an instance of X?
class X {
get Y() {
return 42;
}
}

8 / 82

What would be the result in the console of running this code?
for (var i = 0; i < 5; i++) {
console.log(i);
}

9 / 82

Which expression evaluates to true?

10 / 82

. How would you use the TaxCalculator to determine the amount of tax on $50?
class TaxCalculator {
static calculate(total) {
return total * 0.05;
}
}

11 / 82

Which statement is the correct way to create a variable called rate and assign it the value 100?

12 / 82

Which statement references the DOM node created by the code shown?
<p class="pull">lorem ipsum</p>

13 / 82

When would the final statement in the code shown be logged to the console?
let modal = document.querySelector('#result');
setTimeout(function(){
modal.classList.remove('hidden);
}, 10000);
console.log('Results shown');

14 / 82

Review the code below. Which statement calls the addTax function and passes 50 as an argument?
function addTax(total) {
return total * 1.05;
}

15 / 82

Which statement selects all img elements in the DOM tree?

16 / 82

Which method do you use to attach one DOM node to another?

17 / 82

What is the result in the console of running the code shown?
var start = 1;
function setEnd() {
var end = 10;
}
setEnd();
console.log(end);

18 / 82

You're adding error handling to the code shown. Which code would you include within the if statement to specify an error message?
function addNumbers(x, y) {
if (isNaN(x) || isNaN(y)) {
}
}

19 / 82

. You've written the event listener shown below for a form button, but each time you click the button, the page reloads. Which statement would stop this from happening?
button.addEventListener(
'click',
function (e) {
button.className = 'clicked';
},
false,
);

20 / 82

Why would you choose an asynchronous structure for your code?

21 / 82

What is the output of this code?
var obj;
console.log(obj);

22 / 82

How does the forEach() method differ from a for statement?

23 / 82

Why might you choose to make your code asynchronous?

24 / 82

Your code is producing the error: TypeError: Cannot read property 'reduce' of undefined. What does that mean?

25 / 82

When would you use a conditional statement?

26 / 82

If you attempt to call a value as a function but the value is not a function, what kind of error would you get?

27 / 82

What is one difference between collections created with Map and collections created with Object?

28 / 82

. What is the value of dessert.type after executing this code?
const dessert = { type: 'pie' };
dessert.type = 'pudding';

29 / 82

What's one difference between the async and defer attributes of the HTML script tag?

30 / 82

What is the result in the console of running this code?
'use strict';
function logThis() {
this.desc = 'logger';
console.log(this);
}
new logThis();

31 / 82

You need to match a time value such as 12:00:32. Which of the following regular expressions would work for your code?

32 / 82

Which statement sets the Person constructor as the parent of the Student constructor in the prototype chain?

33 / 82

Why is it usually better to work with Objects instead of Arrays to store a collection of records?

34 / 82

Which event is fired on a text field within a form when a user tabs to it, or clicks or touches it?

35 / 82

Which class-based lifecycle method would be called at the same time as this effect Hook?

useEffect(() => {
// do things
}, []);

36 / 82

What is the result of running this statement?
console.log(typeof(42));

37 / 82

Which Variable-defining keyword allows its variable to be accessed (as undefined) before the line that defines it?

38 / 82

0 && hi

39 / 82

What is the result of running this code?
sum(10, 20);
diff(10, 20);
function sum(x, y) {
return x + y;
}

let diff = function (x, y) {
return x - y;
};

40 / 82

For the following class, how do you get the value of 42 from "X" ?
class X {
get Y() {
return 42;
}
}
var x = new X();

41 / 82

Which of the following operators can be used to do a short-circuit evaluation?

42 / 82

Why would you include a "use strict" statement in a JavaScript file?

43 / 82

How do you add a comment to JavaScript code?

44 / 82

How do you import the lodash library making it top-level Api available as the "_" variable?

45 / 82

Which of these is a valid variable name?

46 / 82

. Which Object method returns an iterable that can be used to iterate over the properties of an object?

47 / 82

What does the following expression evaluate to?

[] == [];

48 / 82

What type of scope does the end variable have in the code shown?
var start = 1;
if (start === 1) {
let end = 2;
}

49 / 82

Which variable is an implicit parameter for every function in JavaScript?

50 / 82

Which statement is true about the "async" attribute for the HTML script tag?

51 / 82

Which choice is valid example for an arrow function?

52 / 82

Which method is called automatically when an object is initialized?

53 / 82

Which of the following values is not a Boolean false?

54 / 82

Which concept is defined as a template that can be used to generate different objects that share some shape and/or behavior?

55 / 82

When would 'results shown' be logged to the console?

let modal = document.querySelector('#results');
setTimeout(function () {
modal.classList.remove('hidden');
}, 10000);

56 / 82

How is a forEach statement different from a for statement?

57 / 82

How does a function create a closure?

58 / 82

Which method converts JSON data to a JavaScript object?

59 / 82

Which keyword is used to create an error?

60 / 82

What is the result in the console of running the code shown?
var Storm = function () {};
Storm.prototype.precip = 'rain';
var WinterStorm = function () {};
WinterStorm.prototype = new Storm();
WinterStorm.prototype.precip = 'snow';
var bob = new WinterStorm();
console.log(bob.precip);

61 / 82

How would you reference the text 'avenue' in the code shown?
let roadTypes = ['street', 'road', 'avenue', 'circle'];

62 / 82

Which choice is not a unary operator?

63 / 82

What will be logged to the console?
'use strict';
function logThis() {
this.desc = 'logger';
console.log(this);
}
new logThis();

64 / 82

. How many prototype objects are in the chain for the following array?
let arr = [];

65 / 82

After the following code, what is the value of a.length?
var a = ['dog', 'cat', 'hen'];
a[100] = 'fox';
console.log(a.length);

66 / 82

What is the name of a function whose execution can be suspended and resumed at a later point?

67 / 82

Which statement creates a new object using the Person constructor?

68 / 82

What is the result in the console of running this code?
function logThis() {
console.log(this);
}
logThis();

69 / 82

Which property references the DOM object that dispatched an event?

70 / 82

Which statement is true about Functional Programming?

71 / 82

What will this code log in the console?
function sayHello() {
console.log('hello');
}

console.log(sayHello.prototype);

72 / 82

What will the value of y be in this code:
const x = 6 % 2;
const y = x ? 'One' : 'Two';

73 / 82

You've written the code shown to log a set of consecutive values, but it instead results in the value 5, 5, 5, and 5 being logged to the console. Which revised version of the code would result in the value 1, 2, 3 and 4 being logged?
for (var i = 1; i <= 4; i++) {
setTimeout(function () {
console.log(i);
}, i * 10000);
}

74 / 82

What two values will this code print?
function printA() {
console.log(answer);
var answer = 1;
}
printA();
printA();

75 / 82

What will be logged to the console?
var a = ['dog', 'cat', 'hen'];
a[100] = 'fox';
console.log(a.length);

76 / 82

Which statement creates a new function called discountPrice?

77 / 82

Which statement represents the starting code converted to an IIFE?

78 / 82

Which choice is an incorrect way to define an arrow function that returns an empty object?

79 / 82

Which collection object allows unique value to be inserted only once?

80 / 82

This program has a problem. What is it?

var a;
var b = (a = 3) ? true : false;

81 / 82

Which of the following is not a keyword in JavaScript?

82 / 82

What is the result of running the statement shown?
let a = 5;
console.log(++a);

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