Top 55 JavaScript Interview Questions & Answers: A Guide for Freshers and Beginners, Exercises of Computer Science

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Top 55

JavaScript

Interview Questions

& Answers

JavaScript Interview Questions for Freshers & Beginners

1. What is JavaScript?

JavaScript, also known as JS, is a popular dynamic programming language used for front-end development. The primary purpose of using JS on web pages is to show things in a dynamic manner. In front-end development, HTML and CSS are used to show static content on a web page. In scenarios where you need to show dynamic content, animation, interactive maps, etc., the role of JavaScript comes into play. Developers call it the third layer, followed by HTML and CSS. You probably have seen the use of JS if you have gone through websites where additional content gets added without reloading, changing colours on the pages, etc. The use of JavaScript programming is common in website development, and web application development, as well as in servers, browsers, games, etc. Over the years, it has become an in-demand language, and an increasing number of people are learning it with reliable web development course online or offline.

2. What is JavaScript Promise?

A Promise in JavaScript is an object or proxy that sets up the connection between producing code and consuming code. It shows whether the asynchronous operation is pending, fulfilled, or rejected. And if it is fulfilled, it will also show the result.

3. What is JavaScript closure?

When you need access to the features of a function that is located outside the inner function, the role of JS closure comes into play. It is such an option that helps even when the function located outside is closed.

4. What is JavaScript array?

In JS, an array is a variable that can store multiple values. In simple terms, you can say that an array has the ability to store a set of more than one item with the name of a single variable.

5. What are the characteristics of an array in JavaScript?

Following are the main characteristics of JavaScrip array: ● Resizable ● Zero-indexed ● Ability to build shallow copies ● Feature to store collection of different items or data types

For instance, you can call the web page a document. If you want to edit this page in JavaScript, then the role of DOM comes into play.

12. What are operators in JavaScript?

An operator in JS is simply a symbol that is utilized to do specific operations, like addition, subtraction, and more. The operations are done on values and variables, or you can call them operands. Let’s understand it with an example. If you want to add two values, then the “+” operator will be used. 10 + 45: // 55 Here, + is an arithmetic operator, which has added the given values. 10 and 45 are the operands here.

13. What are the different operators in JavaScript?

Below is a list of JavaScript operators with their details:

● Assignment Operators

Used when you need to assign values to variables. Operator Name = Assignment operator += Addition assignment -= Subtraction assignment *= Multiplication assignment /= Division assignment %= Remainder assignment **= Exponentiation assignment

● Comparison Operators

Role of these operators is when you want to do a comparison of two values and then have a result. The result will be a boolean value, showing true or false. Operator Name == Equal to

!= Not equal to === Strict equal to !== Strict not equal to

Greater than = Greater than or equal to < Less than <= Less than or equal to

● Arithmetic Operators

Role of these operators is to do arithmetic calculations. Operator Name

• Addition

• Subtraction

• Multiplication / Division % Remainder ++ Increment

• • Decrement ** Exponential

● Logical Operators

Used to do logical operators. After the operation, it shows a boolean value (true/false) as the result. Operator Name && Logical AND | | Logical OR ! Logical NOT

16. How to write hello world in JS?

This is one of the basic JavaScript interview questions for freshers. Writing a hello world program in JS has three different ways, as discussed here:

● console.log()

// write hello world program in JS console.log('Hello World');

● alert()

// write hello world program in JS alert("Hello, World!");

● document.write()

// writing hello world program in JS document.write('Hello, World!');

17. What is BOM in JavaScript?

BOM stands for Browser Object Model. This is one of the most crucial parts of JavaScript in terms of using it on the web part. It helps you to know the functionalities of a browser using objects. As a result, the JS-based projects can interact with the browser.

18. What are comments in JavaScript?

JS comments are simply used to represent a comment or message related to the code. For example, we can use comments to mention details of the code, recommendations, warnings, etc. It should be noted that the JS engine will neglect the comments.

19. What is runtime environment in JavaScript?

The runtime environment is the place to run or execute a program. This environment can access the objects, libraries, etc. and hence runs the code accordingly. Generally, there are two types of JS environments used by a developer. One is the browser-based runtime environment, and another is the NodeJS-based runtime environment. The browser-based runtime environment makes use of a JS engine, web APIs, an event loop, and the callback queue.

20. What are the advantages of JavaScript?

Following are the primary advantages or benefits of using JavaScript:

● Fast Performance

Since JS is an interpreted language, you don’t have to compile it every single time it runs. As a result, it speeds up the development process. Furthermore, it runs on the client side,

where it doesn’t depend on the server. This again optimizes the performance of the website or web app by avoiding the need for requesting resources from the web server.

● Easy to Understand and Simple

Even if you are a beginner with no knowledge of coding, you will find this language easy to learn. Opting for an offline or online web development course further makes things effortless for you so that you can become well-versed with the complete website and web application development skills.

● Works Well With Other Languages and Systems

JavaScript is an interoperable language which means it runs well with other languages and web technologies.

● Cross-platform Development

There are several JS frameworks that help you to use JavaScript for cross-platform development. For example, you can use React Native framework to use JS for mobile app development. You can use Electron to implement JS for desktop app development.

● Frameworks and Libraries

The wide range of JavaScript libraries and frameworks make it an ideal choice for programmers and developers. The tasks can be performed with minimum efforts, accelerating the development process. In addition, these tools enable plenty of other benefits, like cross-platform development.

21. What is JavaScript used for?

Here are the primary uses and applications of JavaScript:

● Creating Interactive Web Pages

Using JS, developers can make web pages more interactive and appealing. For example, new features can be added that bring some functionalities to the users and also enhance the overall UX. Here are some examples of JavaScript in use on web pages. ● Hover colours on buttons ● Carousel slider ● Images zoom in/out ● Countdown timer ● Animations ● Hamburger menu

24. What is the difference between JavaScript and Java?

There are several differences between Java and JavaScript. Whether you are a fresher or an experienced professional, this is among the top JavaScript interview questions for you. Below, we have curated a tabular comparison of Java vs JavaScript so that it becomes easier for you to understand the main differences. Java JavaScript Object-oriented programming language Object-based scripting language Can be used for complicated tasks and processes Can’t be used for complicated tasks Needs code compilation Text-based code Independent language Needs to be used with HTML Strongly typed programming language. Need to declare variables before using them in the program. Loosely typed language. No issues whether data types are declared or not It’s statically-type It’s dynamically-typed High memory consumption Low memory consumption Saved as byte code Saved as source code For concurrency, it uses threads For concurrency, it uses events .java extension used to save programs .js extension used to save programs Supports multithreading Doesn’t support multithreading Objects are based on class Objects are based on prototype Need JDK or Java Development Kit to run the code Need text editor to run the code Primarily used for backend development Can use for both front-end and back-end

25. What was the first name of JavaScript?

During the interview, you can be asked what was JavaScript called when it was developed, or what was the former name of JS. You must be prepared for such JavaScript interview questions and answers. The original name of JavaScript was Mocha when it was developed. It was later changed to LiveScript and then finally became JavaScript.

26. When was JavaScript invented?

It was developed in 1995.

27. What is JavaScript ES6?

ES6 stands for ECMAScript 6. It is a version of JavaScript which was released in 2015. Hence, it is also called ES 2015. There are plenty of new features in JavaScript ES6 compared to the prior versions. These are intended to write better and clean code, while helping developers to get more done with less code.

28. What is a named function in JS?

As the term suggests, a named function is simply a function in JS that has been given a name. This name is given with the use of syntax. The function keyword in JavaScript is used to assign a name to the function or make it a named function. This concept should be in the list of top JavaScript interview questions and answers for freshers.

29. What is an anonymous function?

Unlike named functions, anonymous functions are the ones that do not have any names. Such functions are declared without the use of identifiers. There are certain rules for using an anonymous function in JavaScript. First, you can’t access it right after creating it. For this, you need to use a variable where the anonymous function is saved.

30. What is the difference between JavaScript and JScript?

You need to know the differences between the two as these sound similar. This can be one of the top JavaScript interview questions for freshers. JavaScript JScript A trademark of Oracle Corp. Microsoft owns JScript No support for active content creation Supports active content creation Can manage multi-browser compatibility Supports Internet Explorer only Code runs in browser Code runs only in Internet Explorer Can’t access objects of the browser Can access objects of Internet Explorer Widely used Not popular as it is supported by Internet Explorer only

34. Which method can we use in order to find out the character

from a particular index?

For this, we can use the string charAt() method. For example: var str="WsCube Tech"; document.writeln(str.charAt(3));

35. How can we use an external JavaScript file?

For doing so, we need to add the below-mentioned script tag to the header: Here, wscubetech.js is the name of the external JS file we are looking to use.

36. What is JavaScript prototype?

A prototype in JS is one of the most useful objects using which developers can inherit one object's features to another. You can say that a prototype is linked to all the objects and functions in JS. That’s what it makes capable of inheriting the features of an object.

37. What is the role of JavaScript callback function?

Since numerous actions in JS are asynchronous, these actions are not capable of holding a program from running before completion. Using the callback function, we can define when to run the code.

38. What is the use of window object in JS?

In JavaScript, the window object shows that a window is open in the browser. This object supports all the popular web browsers and therefore the objects, functions, as well as variables are members of the window object. Moreover, you can say that the global variables of JS are considered properties, whereas the global functions are considered methods of the window.

39. What is the use of history object in JavaScript?

The use of the JS history object is to find the web URLs that a user has visited in the browser. In addition, it also helps in browsing the last and next pages, as well as specific pages that a user has visited. As an important property of the window object, the history object is accessible by: ● window.history ● history

40. How to use JavaScript in HTML?

The primary purpose behind using JavaScript on HTML pages is to make them interactive and dynamic. For adding JS code to HTML code, the _

45. Why do we use strict mode in JS?

The purpose of using strict mode in JavaScript is to create silent errors. It helps in building an expression named ‘use strict’ so that we can easily enable the strict mode. Using it, we can modify the normal JS semantics, such as converting the silent errors to throw errors. As a result, silent errors can be avoided. In addition, the performance of the code can be improved in several cases when we use the strict mode.

46. What is JavaScript hoisting?

It is a technique in JS that helps in using a variable, function, or class before the code execution or declaring these things. What hoisting in JavaScript does is prioritize the variables, classes, and functions by shifting them to the top level. As a result, you can find their values without code execution. It will not show any errors. In simple words, the role of JS hoisting is to have the feature to call functions, variables, or classes even if you have not defined them in your code.

47. Which are the best JavaScript frameworks?

The top 10 popular frameworks of JavaScript are: ● ReactJS ● AngularJS ● VueJS ● NodeJS ● BackboneJS ● EmberJS ● Meteor ● Polymer ● Mithril ● Aurelia

48. What is an argument object?

An argument object in JavaScript is a set of multiple arguments stored in the form of arrays. This is used at the time of invoking the functions. It is an in-built JS object that can be accessed only inside a function. Also, this function needs to have the values of the arguments being passed.

49. How can you use JS to find the operating system of the client

machine?

We can make use of the navigator.appVersion string to find the client OS version.

50. How can you use JS to modify the background color of an

HTML document?

We can use the following code to do so: __ In place of “blue”, we can use any colour that we intend to use.

51. What is the best way for exception handling in JavaScript?

JS exception handling is performed using try, catch, finally, and throw keywords. Developers can use try or catch blocks to handle exceptions easily.

52. Explain the role of the debugger keyword in JS.

The debugger keyword in JavaScript is used to halt the program’s execution at the point you implement it. It helps you to control the code execution and its flow in a manual manner.

53. What is the syntax of the JavaScript anonymous function?

Here is the syntax for an anonymous function in JavaScript: function() { // Function Body }

54. How can we create a JavaScript function?

The below syntax can be used for creating a function in JS: function function_name(){ //function body }

55. Is it possible to assign an anonymous function to a variable?

Yes. We can do it.

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