An empty element is an HTML element that has no content. Example <br>
The box model in CSS is a fundamental concept that defines how elements are rendered on a web page by organizing them into a rectangular box with several layers.
Below are some of the top JavaScript interview questions for freshers (with proper answers).
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.
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.
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 it helps even when the function located outside is closed.
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.
The following are the main characteristics of the JavaScrip array:
A function in JavaScript is a set of code which is used to do a certain task. It can also be used for calculation. Before using the function, ensure that it is defined somewhere.
The function keyword in JS is used to execute the functions.
An object in JS is like a thing in real life, having some properties, methods, behaviour, etc. For example, a bike is an object with properties like color, brand name, model, etc. The methods of this bike can be a brake, stop, start, drive, etc.
The full form of NaN is Not a Number. So, in simple terms, the isNaN() is a function in JavaScript that is used to check whether a value is a number or not once it is converted to a number.
If the value is Not a Number, it will show true. It should be noted that this function first changes the values to numbers and then checks whether it is NaN or not
Such JavaScript interview questions can be asked to both freshers and experienced developers. So, let’s know the primary differences between client-side scripting and server-side scripting in JavaScript.
| Client-Side | Server-Side |
|---|---|
| Users can see the source code | Users can’t see the source code |
| It serves the requests of the users and shows the content accordingly. | It is used to manage the database and other backend aspects. |
| Dependent on browser | No dependency on browsers |
| Runs on the web browsers | Runs on the web servers |
| Less data security | Strong data security |
Yes. It is a case-sensitive language.
DOM stands for Document Object Model. It is an interface in coding that is used to represent the data and content of a web document. It helps in enabling programs to modify the style, content, and structure of a web document.
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.
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.
Here, + is an arithmetic operator, which has added the given values. 10 and 45 are the operands here.
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Below is a list of JavaScript operators with their details:
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 |
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 |
The role of these operators is to do arithmetic calculations.
| Operator | Name |
|---|---|
| + | Addition |
| – | Subtraction |
| * | Multiplication |
| / | Division |
| % | Remainder |
| ++ | Increment |
| – – | Decrement |
| ** | Exponential |
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 |
Used for concatenation of strings.
| Operator | Meaning |
|---|---|
| typeof | To know the type of the variable |
| instanceof | To know whether an object is an instance of an object type |
Used when you need to do operations with binary numbers.
| Operator | Name |
|---|---|
| & | Bitwise AND |
| | | Bitwise OR |
| ^ | Bitwise XOR |
| ~ | Bitwise NOT |
| >>> | Zero-fill right shift |
| >> | Right Shift |
| << | Left Shift |
Every action that occurs in code or programming is an event. For instance, the loading of a page is an event. Clicks by the end users on a button are an event. The role of events in JavaScript is to make the program understand that some action has been taken and to react accordingly to that action.
The callback is a function in JavaScript. Its role is to work as an argument by getting passed to other functions. When it is passed to the other functions, those functions will also have the argument executed.
The callback is a function in JavaScript. Its role is to work as an argument by getting passed to other functions. When it is passed to the other functions, those functions will also have the argument executed.
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:
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.
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.
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.
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.
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The following are the primary advantages or benefits of using JavaScript:
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.
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.
JavaScript is an interoperable language which means it runs well with other languages and web technologies.
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.
The wide range of JavaScript libraries and frameworks makes 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.
Here are the primary uses and applications of JavaScript:
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.
You can build games using JavaScript that runs on browsers. For example, you can build puzzles, racing games, role-playing games, etc. A few of the popular games running on JavaScript include Angry Birds, CrossCode, Polycraft, HexGL, etc.
In addition to robust and highly-interactive websites, you can also develop web applications using JavaScript. For instance, Google Maps is one such web app where JS is used.
Using the wide range of JavaScript frameworks available today, you can also develop mobile games. For example, React Native is one popular JS framework for app development.
Numerous server-side activities can be managed using JavaScript and relevant frameworks.
Brendon Eich developed JavaScript.
While preparing for the JavaScript interview questions and answers in 2024, don’t forget to know about the main drawbacks or disadvantages of JS.
Compared to other languages, JS is a bit more non-restrictive. Developers need to be attentive so that they can implement everything as required. That’s why good web development courses cover these aspects of JavaScript so that the developers know the best practices.
Since JS runs on the client side in the browser, the debugging options and features are limited.
Again, the client-side running of the language makes it a bit less secure. Developers need to be aware of these aspects of JavaScript so that they don’t leave any space available for attackers.
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 languag |
| 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 |
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.
It was developed in 1995.
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.
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.
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.
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 |
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JavaScript Promise can have any of the three states:
Among the list of JavaScript interview questions for 3 years experience or above, keep such concepts and learn about them.
It is used when you want to prevent the default action of elements in the browser. You must know that not all actions can be cancelled, and is applicable to only cancellable events.
Syntax:
It is used to stop the propagation of the parent element so that it can not find access to specified events.
Syntax:
There are three ways to create a JavaScript object:
| Ways | Syntax |
|---|---|
| Object literal | object={property1:value1,property2:value2…..propertyN:valueN} |
| Using new keyword | var objectname=new Object(); |
| Using object constructor | var objectname=new Object(); |
For this, we can use the string charAt() method.
For example:
For doing so, we need to add the below-mentioned script tag to the header:
Here, test.js is the name of the external JS file we are looking to use.
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.
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.
In JavaScript, the window object shows that a window is open in the browser. This object supports all the popular web browsers; therefore, the objects, functions, and 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.
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:
The primary purpose behind using JavaScript on HTML pages is to make them interactive and dynamic.
For adding JS code to HTML code, the <script> tag is used. The JS code that you want to add to the HTML is used within the <script> tag, whether you want to place it in the <head> or <body> section.
This method is recommended for small codes. However, for JS scripts that are heavy, it would be great to opt for a dedicated JavaScript file. It helps you to reduce the overall maintenance of the site, differentiates the JS code and HTML code, and optimizes the loading speed.
If you have been a developer using JS for quite some time now, then this can be among the top JavaScript interview questions for experienced professionals. You must know that there are a couple of good reasons to use comments in JavaScript.
Whether you are a beginner or someone with experience, knowing the different types of comments in JavaScript is important. It’s because this can be among the top interview questions on JavaScript for freshers and experienced bot
To answer, start by saying that there are two types of comments.
These comments are written with two forward slashes (//) before your message of the comment. You can use single-line comments before and after the statement.
Before statement
After statement
Usually, the developers prefer multi-line comments more because these can be used to represent single lines and multiple lines of comments both.
For using it, you need to use a forward slash with an asterisk (at the opening of the comment), and an asterisk with a forward slash (at the closing of the comment).
Example:
null in JS is an object which is used to represent that a variable doesn’t have any value. This is not available by default. The developer needs to do it intentionally.
Whereas, undefined is a global object in JS which means that the declared variable has not been assigned any value.
As you might know, the meaning of void is empty. In the case of JS, the void is actually an operator with its role when a function doesn’t return any result. The result it returns will be undefined.
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.
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.
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.
The top 10 popular frameworks of JavaScript are:
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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.
We can make use of the navigator.appVersion string to find the client OS version.
We can use the following code to do so:
In place of “blue”, we can use any colour that we intend to use.
JS exception handling is performed using try, catch, finally, and throw keywords. Developers can use try or catch blocks to handle exceptions easily.
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.
Here is the syntax for an anonymous function in JavaScript:
The below syntax can be used for creating a function in JS:
Yes. We can do it.