JavaScript is a popular programming language that is used to provide dynamic interactivity to websites. Today, JavaScript is one of the most in-demand skills worldwide, creating huge job opportunities for freshers as well as experienced professionals.
Q1. What are the major advantages of JavaScript?
Ans. JavaScript is a programing language used for the web. It can alter the HTML content, attribute values, and CSS style. It can also Show/Hide HTML elements. Some of the other advantages of JavaScript are:
| Advantages | Description |
| Speed | Excellent speed as it immediately runs within the client-side browser. |
| Interoperability | Sound functionality with other programming languages. Easily embedded into any web page. |
| Third-Party Add-ons | Known for its extended functionality. It supports third-party add-ons to build JavaScript applications. |
| Rich-Interface | Used to include items like a drag, drop, and sliders to present a rich interface to users/visitors. |
| Web Presence | JS has a popular web presence. StackOverflow and GitHub extensively use JavaScript. |
| Versatile | Capable of both Front-end (NodeJS) and Back-end development (Angular JS, React JS) |
Q2. How can you differentiate JavaScript from Java?
Ans. The differences between JavaScript and Java are:
| Difference | Java | JavaScript |
| Language | Object-Oriented Programming Language | Object-Oriented Scripting Language |
| Platform | Runs in JVM | Runs on a Web Browser |
| Compilation | Programs are compiled and Interpreted | Only integrated |
| Support | Supported by maximum operating systems | Supported by web browser with different OS |
| Scope | Uses block-based scoping | Uses function-based scoping |
Q3. How to create an object in JavaScript?
Ans. Objects are the building blocks of modern JavaScript and are more of a reference data type.
| Object Creating Ways | Code |
| Object() | var d = new object(); |
| Object.create () | Var a = Object.create(null); |
| Function Constructor | var Obj = function(name) { this.name = name } var c = new Obj(“Hi”); |
Q4. What is the method to change the title of a page using JavaScript?
Ans. Generally, the page title varies based on the HTML document and the element structure. We can give id to an element and use code:
document.getElementById(‘page-title-id’).innerHTML=NewTitle;
Q5. Tell some of the widely used JavaScript testing frameworks.
Ans. This is one of the popular JavaScript interview questions for freshers.
Some of the widely used JS Frameworks are –
- Mocha
- Jest
- Jasmine
- Karma (Test Runner)
- Nightwatch
- Puppeteer (Node Library)
Q6. Define some of the most prevalent JavaScript operators.
Ans. In JavaScript, operators are the symbols that help in performing different operations on the given data.
- Arithmetic operators (+, -, *, /, %, ++, –)
- Comparison operators (==, ===, !=, <,>, >=,<=)
- Assignment operators (=, +=, -=, *=)
- Logical operators – for
var a=10, b=20;
(a !=b) && (a<b); // RETURNS TRUE
Q7. JavaScript Functions – What do you know about it?
Ans. Something that performs a task to produce meaningful outputs is called function. JavaScripts also work on the concepts of both in-built JavaScript functions as well as user-defined functions.
Some of the common JavaScript Functions rules are:
- It should begin with the keyword function
- User-defined functions must have a unique name
Q8. What are some of the JavaScript data types?
Ans. Generally, there are 7 data types in JavaScript:
- Number let n =789;
- String let str = “Hello”;
- Boolean (‘True’ and ‘False’)
- Null let gender = null;
- Undefined (for unassigned values)
- Objects and Symbols (for complex data structures)
- Typeof operator (returns type of argument)
Q9. Describe different types of errors present in JavaScript.
Ans. In JavaScript, there are three different types of errors in programming.
- Parsing errors – Also called Syntax errors, these errors occur at interpretation time in JavaScript. It only affects the tread in which this error occurs, leaving other threads unaffected.
- Run-time errors – Errors that appear at the time of execution and are also defined as exceptions.
- Logical errors – These are some of the most difficult types of errors and occur whenever there are flaws in logic that drive the script. Catching these errors is a very difficult task.
Q10. Can you redirect a page to another page using JavaScript? How?
Ans. Yes, it is possible to redirect a page to another page or URL using JavaScript by using location, replace, and location.assign.
Q11. Define JavaScript and mention some of its features.
Ans. This is one of the top JavaScript interview questions for freshers in 2022.
JavaScript Definition – Initially known as LiveScript, JavaScript is an almost two decades old dynamic programming language used for web pages allowing client-side interaction.
Some Exceptional JavaScript features are-
- Highly useful while using forms
- Platform independent
- Unique built-in features for handling date and time
- Includes rich interfaces like drag and drop
Q12. State the major difference between a programming language and a scripting language. Also tell, JavaScript is which form of language?
Ans. Programming languages are designed to take full usage of any language, and at the same time, scripting languages are designed to fast-pace the coding. JavaScript is a scripting language.
Some of the major differences between both the languages are-
| Scripting Language | Programming Language |
| Uses Interpreter | Uses Compiler |
| Supports Script | Consists of instructions for a computer |
| Combines existing components | Develops from Scratch |
| Needs another program to run | Runs independently |
Q13. What is the difference between Primitives and Objects in JS?
Ans. In JavaScript, values are of two types – Primitives and Objects. Some common differences between both are:
| Objects | Primitives |
| Mutable at the time of coding | Immutable |
| Have a unique identity | No individual identity |
| Compared by reference | Compared by Value |
Q14. What do you understand about the prompt() method?
Ans. Whenever you want to display a dialog with an optional message that prompts the user to input some text, the prompt() method is used. All major browsers including Google Chrome, Internet Explorer, and Firefox., support this
Q15. In JavaScript, what is ‘This’ keyword?
Ans. In JavaScript, the keyword ‘this’ refers to the object it belongs to and gives different values depending upon its usage.
For Example:
- In method – refers to own object
- Alone – refers to the global object
- Function – undefined (in strict mode)
Q16. What are the types of JavaScript Function Scope?
Ans. Basically, the scope circumscribes the variable’s visibility. Talking about JavaScript, functions are first-class objects holding properties like an object. The only difference is that these functions can be called, unlike other objects. JavaScript covers majorly two types of Function Scope:
- Local Scope – Variables defined inside the functions are called local to the function.
- Global Scope – The outside area of all functions is considered global.
Q17. What is the difference between JavaScript keywords – var and let.
Ans. In JavaScript, var and let are used for variable deceleration, but var is known as function scope whereas, let is known as block scoped.
Q18. What do you mean by Hoisting in JS?
Ans. The concept of hoisting stands for uplifting the variable and functions on the top of their scope before the code execution takes place. In the JavaScript mechanism, no matter wherever the functions are declared, they are taken on the topmost position, immaterial of their scope – global or local.
Q19. Name a few built-in methods.
Ans. JavaScript has several built-in methods which are classified as:
- Number Methods – constructor(), toExponential(), toFixed()
- Boolean Methods – toSource(), toString(), valueOf()
- Date Methods – Date(), getFullYear(), getHours()
- Math Methods – abs(), exp(), log()
Q20. How can you submit a form using JS?
Ans. To submit a simple form, the below code will work.
document.form[0].submit();
Q21. What do you mean by control flow and error handling in JS?
Ans. In JavaScript, control flow stands for a process that ensures that an appropriate order is followed to execute statements in a script. It also ensures that one must read not only the entire code but also check the program structure and how that structure affects execution.
Whereas, error handling in JS means catching an error using “try..catch” Initially, the code try functions in a way that if the code is error-free, the catch function will be ignored. But in case any error is found, try execution is paused, and control(err) begins.
Q22. What is DOM in JS?
Ans. DOM stands for Document Object Modeling, which is a language allowing dynamic accessing and modifying the content in any document. Level of abstractions DOM has in JavaScript:
- DOM Level 1
- DOM Level 2
- DOM Level 3
- Scalable Vector Graphics
- Mathematical Mark-up Language
Q23. What is BOM in JS?
Ans. BOM stands for Browser Object Model. It is an extensive representation of elements provided by the browser like document, location, history, and frames exposed to JavaScript. It includes the properties and methods for JavaScript to interact with the web browser. The window is the top-level object in the BOM, representing the browser window. It contains all other browser objects, including the properties and methods that can be used to control the Web browser. The important BOM objects are document, history, screen, navigator, location, and frames.
You can call all the functions of the window by specifying the window or directly. To access the document, one can use a code document or window.document.
Q24. What is a JavaScript string?
Ans. Whenever we want to store or manipulate text, we use JavaScript strings. We need JavaScript String methods to work with strings.
Q25. In JavaScript, what does an Anonymous function do?
Ans. The function that has no defined name is called an anonymous function in JavaScript. One can easily use this function by replacing expression. This anonymous function can also be assigned to a variable. Further, this function can also be moved as an argument to a different function.
Q26. In JavaScript, how can you validate null or empty values?
Ans. This is one of the top Javascript interview questions and answers for freshers.
It is essential to check the condition that any user has added any value in the given field. The below code will help:
// If the length is 0 then imitate helper message
function required(input)
{
if (input.value.length == 0)
{
alert(“message”);
return false;
}
return true;
}
Q27. List some of the Design Patterns in JS.
Ans. Whenever somebody wants to reuse solutions for regularly occurring problems in software designing, Design Patterns will solve the purpose.
The latest Design Patterns in JS are:
- Module Design pattern
- Revealing Module pattern
- Prototype Design pattern
- Revealing Prototype pattern
- Observer Design pattern
- Singleton
Q28. Define the usage of Set objects in JavaScript.
Ans. Set objects in JavaScript are the source to store elements having unique values, including both primitive as well as object reference values.
Q29. Explain Deep vs shallow object copying in JavaScript.
Ans.
- Deep Coping – This means that all the values of the existing/original variables are copied to a new variable and, thus, disconnected from the existing variables.
- Shallow Coping – When commanded for shallow coping, not all the existing variables are disconnected, and some values or sub-values are still connected to the original.
Let’s move on to some intermediate and advanced-level top JavaScript interview questions for 2023.
Q30. How to formulate a cookie using JS?
Ans. A cookie is a set of data saved on the computer and accessed by the browser.
Step to create a JavaScript cookie :
document.cookie = “cookiename=John”; expires = date”;
Q31. Define isNaN in JS.
Ans. isNaN is a function that determines whether a value is NaN (not-a-number) or not. It is used for defining a function true if in case the argument is not a number. returns true if the value equates to NaN. Otherwise, it returns false.
Syntax:
isNaN(value)
Q32. Which method is used to remove focus from the specified object in JS?
Ans. The Blur method removes focus from the specified object in JS.
