JavaScript Quiz – JavaScript MCQ Online Test

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Contenders who want to learn the basics of the JavaScript must focus on this page. Also, candidates can practice the JavaScript Quiz. People who want to get through from the interview or else form the competitive exams regarding the Technical section. Then they can practice the given JavaScript MCQ in this section. We also offer the JavaScript Programming Quiz that helps you to overcome the issues facing the written test part. So, we advise aspirants to move forward to learn the essential element and then practice the JavaScript Online Test. We have given you the commonly asked JavaScript Multiple Choice Questions that they can have the apparent explanation for each question.

Details About JavaScript Quiz

Aspirants while participating in this JavaScript Online Test, they must know the necessary information about what we provide. We embedded all the details of the JavaScript Programming Quiz like the name of the quiz and also the number of questions given for the test. Moreover, it specifies the type of the exam.

JavaScript MCQ Quiz Instructions

Every individual while attempting the JavaScript Interview Questions they should know the instruction for such exam. So, one should follow the instruction must and should to complete the test in right way.

• Moreover, the test is of Multiple Choice Type, and students can choose the correct answer to the question in the given four option.
• So, contenders make a note of it and then try to complete this test as soon as possible within time.
• Furthermore, there is no negative marking too.

JavaScript Online Test

What is the correct way to declare a variable in JavaScript?
A) let x = 10;
B) const y = 20;
C) var z = 30;
D) All of the above

Answer: D) All of the above

Explanation: In JavaScript, you can declare a variable using the let, const, or var keyword. The let and const keywords were introduced in ECMAScript 6 (ES6) and are used for declaring block-scoped variables, whereas the var keyword is used for declaring function-scoped variables.

What is the output of the following code snippet?
console.log(2 + ‘2’);

A) 4
B) 22
C) ’22’
D) NaN

Answer: C) ’22’

Explanation: In JavaScript, when you concatenate a string with a number, the number is implicitly converted to a string. Therefore, the expression ‘2’ + 2 results in the string ’22’.

What is the correct way to check if a variable is an array in JavaScript?
A) Array.isArray(arr)
B) typeof arr === ‘array’
C) arr instanceof Array
D) Both A and C

Answer: D) Both A and C

Explanation: In JavaScript, you can use the Array.isArray() method or check the instanceof operator with Array to determine if a variable is an array.

What is the purpose of the ‘use strict’ directive in JavaScript?
A) To enable strict mode, which enforces stricter parsing and error handling
B) To allow the use of modern JavaScript features
C) To enable debugging mode
D) To enable ES6 syntax

Answer: A) To enable strict mode, which enforces stricter parsing and error handling

Explanation: ‘use strict’ is a directive that enables strict mode in JavaScript. Strict mode enforces stricter parsing and error handling, helps to prevent common programming mistakes, and disables certain features that are considered error-prone or unsafe.

What is the output of the following code snippet?
console.log(0.1 + 0.2 === 0.3);

A) true
B) false
C) NaN
D) SyntaxError

Answer: B) false

Explanation: Due to floating-point precision limitations in JavaScript, the expression 0.1 + 0.2 does not exactly equal 0.3. Therefore, the comparison 0.1 + 0.2 === 0.3 evaluates to false.

What is the purpose of the ‘async’ keyword in JavaScript?
A) To declare a function as asynchronous, which returns a promise
B) To declare a function as synchronous, which returns a callback
C) To declare a function as a generator
D) To declare a function as a constructor

Answer: A) To declare a function as asynchronous, which returns a promise

Explanation: The ‘async’ keyword in JavaScript is used to declare a function as asynchronous, meaning that it returns a promise. This allows the function to perform asynchronous operations, such as making HTTP requests, and handle them using the async/await syntax or promise chaining.

What is the correct way to define a function in JavaScript?
A) function myFunction() {}
B) myFunction() => {}
C) () => myFunction {}
D) const myFunction = function() {}

Answer: A) function myFunction() {}

Explanation: The correct way to define a function in JavaScript is using the function declaration syntax, as shown in option A. Options B, C, and D represent other forms of function syntax, such as arrow functions and function expressions, but the function declaration syntax (option A) is the most common and traditional way to define a function in JavaScript.

Which of the following is not a valid JavaScript data type?
A) Object
B) Null
C) Undefined
D) Double

Answer: D) Double

Explanation: In JavaScript, ‘Double’ is not a valid data type. The valid primitive data types in JavaScript are Number, String, Boolean, Null, and Undefined, while the Object data type is a reference type.

What is the correct way to create a shallow copy of an array in JavaScript?
A) const newArray = originalArray;
B) const newArray = […originalArray];
C) const newArray = originalArray.slice();
D) All of the above

Answer: B) const newArray = […originalArray];

Explanation: Option B uses the spread operator (…) to create a shallow copy of the originalArray. This creates a new array with the same elements as the original array, but they are separate references in memory. Options A and C simply create a reference to the original array, so any changes made to newArray will also affect the originalArray.

What does the ‘this’ keyword refer to in JavaScript?
A) It always refers to the global object
B) It refers to the object on which the current method was called
C) It refers to the parent object of the current object
D) It refers to the JavaScript engine

Answer: B) It refers to the object on which the current method was called

Explanation: In JavaScript, the ‘this’ keyword refers to the object on which the current method was called. The value of ‘this’ is determined at runtime based on how the function was invoked, such as through an object’s method or using call/apply/bind methods.

What is the purpose of the ‘bind()’ method in JavaScript?
A) To create a new function with a specific context for ‘this’
B) To bind event listeners to DOM elements
C) To create a copy of an object
D) To bind a function to a specific scope

Answer: A) To create a new function with a specific context for ‘this’

Explanation: The ‘bind()’ method in JavaScript is used to create a new function with a specific context for ‘this’. It allows you to set the value of ‘this’ explicitly when invoking the function, regardless of how the function is called. This is useful in cases where you want to ensure that a function always has a specific context for ‘this’.

What is the correct way to handle errors in JavaScript using try-catch block?
A) try { // code to be executed } catch (error) { // handle error }
B) catch (error) { // code to be executed } try { // handle error }
C) try { // code to be executed } catch { // handle error }
D) catch { // code to be executed } try { // handle error }

Answer: A) try { // code to be executed } catch (error) { // handle error }

Explanation: The correct way to handle errors in JavaScript using a try-catch block is shown in option A. The try block contains the code that might throw an exception, and the catch block is used to handle the error by providing an error object as an argument, which contains information about the error that occurred. Options B, C, and D have incorrect syntax for try-catch block.

What is the purpose of the ‘localStorage’ object in JavaScript?
A) To store data on the server
B) To store data on the client-side, which persists even after closing the browser
C) To store data temporarily in memory
D) To store data in a cache

Answer: B) To store data on the client-side, which persists even after closing the browser

Explanation: The ‘localStorage’ object in JavaScript is used to store data on the client-side, specifically in the web browser’s local storage. Unlike session storage, which is temporary and cleared when the browser is closed, data stored in ‘localStorage’ persists even after closing the browser or restarting the computer. This makes it useful for storing data that needs to be accessed across different sessions or even across different web pages.

What is the difference between ‘null’ and ‘undefined’ in JavaScript?
A) They are interchangeable and can be used interchangeably
B) ‘null’ is used to represent an empty or non-existent value, while ‘undefined’ is the default value of a variable that has not been assigned a value
C) ‘undefined’ is used to represent an empty or non-existent value, while ‘null’ is the default value of a variable that has not been assigned a value
D) There is no difference, both represent the absence of a value

Answer: B) ‘null’ is used to represent an empty or non-existent value, while ‘undefined’ is the default value of a variable that has not been assigned a value

Explanation: In JavaScript, ‘null’ is a special value that represents an empty or non-existent value, whereas ‘undefined’ is a default value assigned to a variable that has been declared but has not been assigned any value. They are not interchangeable and have different use cases. ‘null’ is typically used when you want to explicitly set a variable to have no value, while ‘undefined’ is usually used when a variable has not been assigned a value yet.

What is the purpose of the ‘event.preventDefault()’ method in JavaScript?
A) To stop the propagation of an event
B) To prevent the default behavior of an event
C) To trigger an event
D) To add an event listener to an element

Answer: B) To prevent the default behavior of an event

Explanation: The ‘event.preventDefault()’ method in JavaScript is used to prevent the default behavior of an event. For example, when an event is triggered by an element, such as clicking on a link or submitting a form, the default behavior of that event may include navigating to a new page or submitting the form, respectively. By calling ‘event.preventDefault()’, you can prevent the default behavior from occurring and provide custom behavior for the event.

Which of the following is not a valid way to declare a JavaScript variable?
A) const myVar = 10;
B) let myVar = 20;
C) var myVar = 30;
D) myVar = 40;

Answer: D) myVar = 40;

Explanation: Option D is not a valid way to declare a JavaScript variable because it does not use any of the valid keywords (‘const’, ‘let’, or ‘var’) to declare the variable. In JavaScript, variables must be declared using ‘const’, ‘let’, or ‘var’ keywords before they can be assigned a value.

What is the purpose of the ‘setTimeout()’ function in JavaScript?
A) To delay the execution of a function by a specified time
B) To execute a function repeatedly at a specified interval
C) To set a timeout for a network request
D) To define a callback function

Answer: A) To delay the execution of a function by a specified time

Explanation: The ‘setTimeout()’ function in JavaScript is used to delay the execution of a function by a specified time, measured in milliseconds. It takes a function as its first argument and a time delay as its second argument, and schedules the function to be executed after the specified delay. This is often used for tasks such as animating elements or adding a delay before executing certain logic in a program.

Which of the following is not a valid type of error in JavaScript?
A) SyntaxError
B) TypeError
C) LogicError
D) ReferenceError

Answer: C) LogicError

Explanation: Option C is not a valid type of error in JavaScript. SyntaxError occurs when there is a mistake in the syntax of the code, TypeError occurs when a value of an unexpected type is used, and ReferenceError occurs when trying to access an undeclared or undefined variable. However, LogicError is not a predefined error type in JavaScript. It is a generic term used to refer to logical mistakes in the code that do not result in a specific error type.

What is the purpose of the ‘bind()’ method in JavaScript?
A) To create a new array with the results of calling a function on every element in an array
B) To attach an event listener to an element
C) To create a new function with a specified ‘this’ value and initial arguments
D) To add a property to an object

Answer: C) To create a new function with a specified ‘this’ value and initial arguments

Explanation: The ‘bind()’ method in JavaScript is used to create a new function with a specified ‘this’ value and initial arguments. It allows you to set the value of ‘this’ explicitly for a function, regardless of how or where it is called. This can be useful when you want to create a function with a specific context, such as passing a method as a callback function, or when you want to partially apply arguments to a function to create a new function with a subset of arguments.

What is the purpose of the ‘JSON.parse()’ method in JavaScript?
A) To convert a JavaScript object to a JSON string
B) To parse a JSON string and convert it into a JavaScript object
C) To validate the syntax of a JSON string
D) To stringify a JavaScript object

Answer: B) To parse a JSON string and convert it into a JavaScript object

Explanation: The ‘JSON.parse()’ method in JavaScript is used to parse a JSON (JavaScript Object Notation) string and convert it into a JavaScript object. JSON is a lightweight data-interchange format that is commonly used to exchange data between a client and a server. The ‘JSON.parse()’ method takes a JSON string as its argument and returns a JavaScript object that represents the parsed data. This allows you to easily work with data in JSON format in your JavaScript applications.

About JavaScript

In general, javascript is scripting language as well as dynamic computer programming language. Moreover, it is lightweight and used for the part of web page designing. And implement the client-side script to interact with the user. Mostly this language is to design the dynamic pages. Also, this language is also known as the LiveScript and changed like javascript by the Netscape. To know more info about JavaScript Quiz must read the entire article. Furthermore, the general-purpose core of the language has been embedded in Netscape, Internet Explorer, and other web browsers. Also, the ECMA-262 Specification defined the standard version of the core JavaScript language. The following are the features of JavaScript

• JavaScript is a lightweight, interpreted programming language.
• Designed for creating network-centric applications.
• Complementary to and integrated with Java.
• Interpreted Programming Language with the object-oriented capabilities.
• Complementary to and integrated with HTML.
• Open and cross-platform

The Advantages of JavaScript programming language are

• Less server interaction
• Increased interactivity
• Immediate feedback to the visitors
• Richer interfaces

Benefits Of Practicing The JavaScript Quiz

• JavaScript Interview Questions helps you to improve your coding skills.
• Increases your logical and thinking ability.
• Contenders can have capable to attempt any type of JavaScript Programming Quiz better after this test.
• Also, we provide you the apt explanation for each question whether it is right or wrong.

How To Check JavaScript Programming Online Test Results

Candidates after the submission of the test, don’t go away and stay here for better results. Also, the marks are in the form of the ranks or grades. So, please check the appropriate explanation for every question and note them to recover the mistakes in future.

Hereby, we enclose that we provide more information and also exciting questions relevant to the JavaScript Quiz. You need to do is follow our Freshers Now website.