Top 10 Javascript Interview Questions & Answers

WAs a candidate for JavaScript (Web development) you would definitely like to know the best possible questions you might face in your next Javascript interview. Thought the questions change from one interviewer to another, we would like to put together a set of questions considering that it is expected from you to know the correct answers to these questions.

List of Top Javascript Freelancers

Question 1

What is JavaScript?

Answer: JavaScript is an object-oriented computer programming language commonly used to create interactive effects within web browsers. It is primarily a Client side scripting language and the script is inserted into HTML pages.

*Tip: It is good to mention whether a particular language is primarily client side or server side

Question 2

What are key differences between Java and JavaScript?

Answer: Java is an Object oriented programming language while JavaScript is an Object oriented scripting language. Java creates applications that run in a virtual machine or browser while JavaScript code is run on a browser only. Java code needs to be compiled while JavaScript code are all in text.

*Tip: Difference between languages with similar names are common questions

Question 3

Tell me some of the best practices while writing JavaScript code

Answer: Some of the best practices I follow in JavaScript are –

• Avoid Global variables
• Declare Local variables
• Initialise variables when you declare them
• Put all declaration at the top of each script or function

*Tip: Best practices in any programming languages are often asked by organisations who value best coding practices for efficient programming

Question 4

What is a JavaScript function and how is it defined? Give an example.

Answer: A JavaScript function is a block of code designed to perform a particular task. A JavaScript function is executed when it is invoked (or called)

function ProdFunction(x1, x2) {

   return x1 * x2;             // The function returns the product of x1 and x2

}

*Tip: Being ready with small code snippets is always handy during interviews

Question 5

What is static and dynamic web site design and can you use JavaScript in both cases?

Answer: A static site is one that is usually written in plain HTML and what is in the code of the page is what is displayed to the user.

A dynamic site is one that is written using a server-side scripting language such as PHP, ASP, JSP, or ColdFusion. In such a site the content is called in by the scripting language from other files or from a database depending on actions taken by the user.

JavaScript is primarily a client side scripting so it’s more useful in static web sites

*Tip: Web development basic will be checked during any interview related to a web based technology

Question 6

What is the syntax of do-while loop in JavaScript?

Answer: The syntax for do-while loop in JavaScript is as follows −

do{

   Statement(s) to be executed;

} while (expression);

*Tip: Don’t miss the semicolon used at the end of the do…while loop.

Question 7

How is JQuery related to JavaScript?

Answer: JavaScript and jQuery are actually the same thing. In a nutshell, jQuery is a set of JavaScript libraries that have been designed specifically to simplify HTML document traversing, animation, event handling, and Ajax interactions.

*Tip: Questions about similar technologies will always get mixed with each other.

Question 8

What are some of the advanced techniques used in JavaScript?

Answer: Using Recursion is an important programming technique, in which a function calls itself.

Using objects and arrays: In JavaScript, objects and arrays are almost identical to each other. The two main differences are that non-array objects do not have an automatic length property, and arrays do not have the properties and methods of an object.

Using Constructors

*Tip: Some of the questions are experienced JavaScript programmers

Question 9

Which functions handle the basic UI operations in JavaScript?

Answer: The three main functions handling user interface in JavaScript are alert, prompt and confirm with syntax as below:

• alert (message)
• result = prompt (text [, default]);
• result = confirm (message)

*Tip: User Interface (UI) is one of the favourite topics for interviewers

Question 10

What is a constructor? Give some examples

Answer: A constructor is a function that instantiates a particular type of Object. You invoke a constructor with the new keyword. Here are a few examples of constructors with built-in JavaScript objects and custom objects.

Examples:

// Creates a generic object.

var myObject = new Object();

// Creates a Date object.

var myBirthday = new Date(1961, 5, 10);

// Creates a user defined object.

var myCar = new Car();

*Tip: Some of the questions are meant for advance users of JavaScript and will not be generally asked if you are a fresher

We hope you have got the gist of important questions which can help you prepare for your interview

All the Best!