JavaScript MCQ With Answers
Javascript is one of the most popular programming languages in the world currently, and it is basically the language of the web. It is a lightweight, cross-platform, and interpreted programming language, primarily used for web development and backend development. Javascript is a language that is used widely on both the client and server sides of development. Javascript offers a vast standard library that has a wide variety of functions and methods available to help in the process of development, making the entire process easier and hassle-free.
Javascript can be added to our HTML code in mostly 2 ways:
- Internal Javascript: Javascript in this case is directly added to the HTML code by adding the JS code inside the <script> tag, which can be placed either inside the <head> or the <body> tags based on the requirement of the user.
- External Javascript: In this case, the Javascript code is written inside an external file with the extension file_name.js, and then the file is linked to the HTML file inside the <head> tag.
Features of Javascript
- Javascript is a lightweight, cross-platform, and interpreted language.
- It was developed with the main intention of DOM manipulation, bringing forth the era of dynamic websites.
- Javascript functions are objects and can be passed in other functions as parameters.
- Can handle date and time manipulation.
- Can perform Form Validation.
- A compiler is not needed.
Useful Resources
- JavaScript Books
- JavaScript Projects
- JavaScript Features
- JavaScript Frameworks
- JavaScript IDE
- JavaScript Libraries
- Difference between Typescript and Javascript
JavaScript MCQ
What will be the output of the following code snippet?
const obj1 = {first: 20, second: 30, first: 50};
console.log(obj1);{first: 20, second: 30}
{first: 50, second: 30}
{first: 20, second: 30, first: 50}
Syntax Error
What will be the output of the following code snippet?
let a = [1, 2, 3, 4, 5, 6];
var left = 0, right = 5;
var found = false;
var target = 5;
while(left <= right) {
var mid = Math.floor((left + right) / 2);
if(a[mid] == target) {
found = true;
break;
}
else if(a[mid] < target) {
left = mid + 1;
}
else {
right = mid - 1;
}
}
if(found) {
print("YES");
}
else {
print("NO");
}YES
NO
Syntax Error
None of the above
What will be the output of the following code snippet?
print(typeof(NaN));
Object
Number
String
None of the above
What will be the output of the following code snippet?
let s = "00000001111111";
let l = 0, r = s.length - 1, ans = -1;
while(l <= r) {
var mid = Math.floor((l + r) / 2);
if(s[mid] == '1') {
ans = mid;
r = mid - 1;
}
else {
l = mid + 1;
}
}
print(ans);8
7
0
1
What will be the output of the following code snippet?
const example = ({ a, b, c }) => {
console.log(a, b, c);
};
example(0, 1, 2);0 1 2
0 Undefined Undefined
Undefined Undefined Undefined
None of the above
What will be the output of the following code snippet?
function solve(arr, rotations){
if(rotations == 0) return arr;
for(let i = 0; i < rotations; i++){
let element = arr.pop();
arr.unshift(element);
}
return arr;
}
// solve([44, 1, 22, 111], 5);[111, 44, 1, 22]
[44, 1, 22, 111]
[111, 44, 1, 22]
[1, 22, 111, 44]
What will be the output of the following code snippet?
var a = Math.max();
var b = Math.min();
print(a);
print(b);-Infinity Infinity
Infinity -Infinity
Infinity Infinity
-Infinity -Infinity
What will be the output of the following code snippet?
const set = new Set();
set.add(5);
set.add('Hello');
set.add({ name: 'Scaler' });
for (let item of set) {
console.log(item + 6);
}11 NaN NaN
11 NaN [object Object]
11 Hello6 [object Object]6
None of the above
What will be the output of the following code snippet?
var a = "hello";
var sum = 0;
for(var i = 0; i < a.length; i++) {
sum += (a[i] - 'a');
}
print(sum);47
NaN
0
None of the above
What will be the output of the following code snippet?
function test(...args) {
console.log(typeof args);
}
test(12);NaN
Number
Object
Array
What will be the output of the following code snippet?
var a = true + true + true * 3;
print(a)3
0
Error
5
What will be the output of the following code snippet?
a = [1, 2, 3, 4, 5];
print(a.slice(2, 4));3, 4
2, 3
3, 4, 5
2, 3, 4
What will be the output of the following code snippet?
var a = 1;
var b = 0;
while (a <= 3)
{
a++;
b += a * 2;
print(b);
}4 10 18
1 2 3
1 4 7
None of the above
What will be the output of the following code snippet?
(function(){
setTimeout(()=> console.log(1),2000);
console.log(2);
setTimeout(()=> console.log(3),0);
console.log(4);
})();1 2 3 4
2 3 4 1
2 4 3 1
4 3 2 1
What will be the output of the following code snippet?
<script type="text/javascript" language="javascript">
var a = "Scaler";
var result = a.substring(2, 4);
document.write(result);
</script>al
ale
cal
caler
When an operator’s value is NULL, the typeof returned by the unary operator is:
Boolean
Undefined
Object
Integer
When the switch statement matches the expression with the given labels, how is the comparison done?
Both the datatype and the result of the expression are compared.
Only the datatype of the expression is compared.
Only the value of the expression is compared.
None of the above.
Which function is used to serialize an object into a JSON string in Javascript?
stringify()
parse()
convert()
None of the above
Which object in Javascript doesn’t have a prototype?
Base Object
All objects have a prototype
None of the objects have a prototype
None of the above
Which of the following are closures in Javascript?
Variables
Functions
Objects
All of the above
Which of the following are not server-side Javascript objects?
Date
FileUpload
Function
All of the above
Which of the following is not a Javascript framework?
Node
Vue
React
Cassandra
Which of the following keywords is used to define a variable in Javascript?
var
let
Both A and B
None of the above
Which of the following methods can be used to display data in some form using Javascript?
document.write()
console.log()
window.alert()
All of the above
Which of the following methods is used to access HTML elements using Javascript?
getElementbyId()
getElementsByClassName()
Both A and B
None of the above
What is the use of the <noscript> tag in Javascript?
The contents are displayed by non-JS-based browsers.
Clears all the cookies and cache.
Both A and B.
None of the above.
How can a datatype be declared to be a constant type?
const
var
let
constant
How do we write a comment in javascript?
/* */
//
#
$ $
How to stop an interval timer in Javascript?
clearInterval
clearTimer
intervalOver
None of the above
Javascript is an _______ language?
Object-Oriented
Object-Based
Procedural
None of the above
The 3 basic object attributes in Javascript are:
Class, prototype, objects' parameters.
Class, prototype, object's extensible flag.
Class, parameters, object's extensible flag.
Classes, Native object, and Interfaces and Object's extensible flag.
The process in which an object or data structure is translated into a format suitable for transferral over a network, or storage is called?
Object Serialization
Object Encapsulation
Object Inheritance
None of the above
Upon encountering empty statements, what does the Javascript Interpreter do?
Throws an error
Ignores the statements
Gives a warning
None of the above
What does the Javascript “debugger” statement do?
It will debug all the errors in the program at runtime.
It acts as a breakpoint in a program.
It will debug error in the current statement if any.
All of the above.
What does the ‘toLocateString()’ method do in JS?
Returns a localised object representation.
Returns a parsed string.
Returns a localized string representation of an object.
None of the above.
What does … operator do in JS?
It is used to spread iterables to individual elements
It is used to describe a datatype of undefined size
No such operator exists
None of the above
What happens when we run this code?
function dog() {
print("I am a dog.");
}
dog.sound = "Bark";Syntax Error
“I am a dog” gets printed
ReferenceError
Nothing happens
What is the output of the following code snippet?
print(NaN === NaN);
true
false
undefined
Error
How are objects compared when they are checked with the strict equality operator?
The contents of the objects are compared
Their references are compared
Both A and B
None of the above
What keyword is used to check whether a given property is valid or not?
in
is in
exists
lies
What keyword is used to declare an asynchronous function in Javascript?
async
await
setTimeout
None of the above
What will be the output for the following code snippet?
<p id="example"></p>
<script>
function Func()
{
document.getElementById("example").innerHTML=Math.sqrt(81);
}
</script>9
81
Error
0
What will be the output of the following code snippet?
(function(a){
return (function(){
console.log(a);
a = 6;
})()
})(21);6
NaN
21
None of the above
What will be the output of the following code snippet?
let n = 24;
let l = 0, r = 100, ans = n;
while(l <= r) {
let mid = Math.floor((l + r) / 2);
if(mid * mid <= n) {
ans = mid;
l = mid + 1;
}
else {
r = mid - 1;
}
}
print(ans);5
4
6
3
What will be the output of the following code snippet?
let sum = 0;
const a = [1, 2, 3];
a.forEach(getSum);
print(sum);
function getSum(ele) {
sum += ele;
}6
1
2
None of the above
What will be the output of the following code snippet?
print(parseInt("123Hello"));
print(parseInt("Hello123"));123 NaN
123Hello Hello123
NaN NaN
123 123
What will be the output of the following code snippet?
var a = Math.max() < Math.min();
var b = Math.max() > Math.min();
print(a);
print(b);true false
false true
true true
false false
What will be the output of the following code snippet?
<script type="text/javascript" language="javascript">
var x=12;
var y=8;
var res=eval("x+y");
document.write(res);
</script>20
x+y
128
None of the above
What will be the output of the following code snippet?
<script type="text/javascript">
a = 5 + "9";
document.write(a);
</script>Compilation Error
14
Runtime Error
59
What will be the output of the following code snippet?
const obj1 = {Name: "Hello", Age: 16};
const obj2 = {Name: "Hello", Age: 16};
print(obj1 === obj2);true
false
Undefined
None of the above
