Most Asked JavaScript Interview Questions -

Most Asked JavaScript Interview Questions with Answers

Are you looking for JavaScript Interview Questions? Are you preparing for JavaScript interview for jobs? This is the right place you have come. Here, we will guide and help you to enhance your JavaScript skills, and to be prepared for the job.

Most of the product based companies ask JavaScript questions in the interview. Here, we are providing a good collection of real-world JavaScript Interview questions which are generally asked. Each question has a perfectly written answer. So, let’s start.

Que 1) What is JavaScript? / What do you understand by JavaScript?

JavaScript is one of the most widely used web development languages. Actually, it is the third biggest web technology after HTML and CSS. JavaScript is a scripting language used to construct online web and mobile apps, web servers, games, etc. It was originally designed to build dynamic web pages but now, it also runs on server and on almost any device that is enabled with JavaScript and has the JavaScript Engine installed.

JavaScript is also an object-oriented programming language. You can create websites, web applications, and mobile applications using JavaScript nowadays. Now, the server-side version of JavaScript is called Node.js. It can be used to create online web and mobile apps, real-time applications, online streaming applications, and videogames. JavaScript provides a lot of inbuilt libraries that can be used to construct desktop and mobile programs. By using these JavaScript libraries, the developers can save a lot of time.

Que 2) What is a script in JavaScript?

A script is a JavaScript program that can be added to the HTML of any web page. When the HTML page loads, these scripts execute automatically.

Que 3) Who has developed JavaScript?

The first version of JavaScript was appeared in 1995. It was designed and developed by Brendan Eich.

Que 4) Is Java and JavaScript same?

As Java and JavaScript both are object-oriented programming languages that are used to generate websites and applications but they are completely different in working and features.

Java is a high-level, class-based, object-oriented general-purpose programming language designed to have as few implementation dependencies as possible. On the other hand, unlike Java, JavaScript is the most widely used web development languages. It was originally designed to build dynamic web pages at first but it is now also used as server language. The server-side version of JavaScript is known as Node.js. JavaScript is a lightweight, cross-platform scripting language. It is widely used for client-side validation. The JavaScript Translator (embedded in the browser) is responsible for translating the JavaScript code for the web browser.

Most Asked JavaScript Interview Questions

Que 5) What are the most possible ways to create objects in JavaScript?

There are several ways to create objects in JavaScript. Some of them are as follows:

Object constructor: This is the simplest way to create an empty object. But this approach is not recommended nowadays.

Example:

var object = new Object();

Object’s create method: This method is used to create a new object by passing the prototype object as a parameter.

Example:

var object = Object.create(null);

Object literal syntax or object initializer: This method is a comma-separated set of name-value pairs wrapped in curly braces.

Example:

var object = {
name: “Rocky”
age: 24
};

Note: This is the easiest way to create an object in JavaScript. Here, object literal property values can be of any data type, such as array, function, and nested object.

Function constructor: In this method, we create any function and apply the new operator to create object instances.

Example:

function Person(name) {
this.name = name;
this.age = 24;
}
var object = new Person(“Rocky”);

Function constructor with prototype: This method is similar to the function constructor but it uses prototype for their properties and methods.

Example:

function Person() {}
Person.prototype.name = “Rocky”;
var object = new Person();

Note: This is equivalent to an instance created with an object create method with a function prototype and then call that function with an instance and parameters as arguments.

function func() {};
new func(x, y, z);
OR
// Create a new instance using function prototype.
var newInstance = Object.create(func.prototype)
// Call the function
var result = func.call(newInstance, x, y, z),
// If the result is a non-null object then use it otherwise just use the new instance.
console.log(result && typeof result === ‘object’ ? result : newInstance);

ES6 Class syntax: This method introduces class feature to create the objects

Example:

class Person {
constructor(name) {
this.name = name;
}
}
var object = new Person(“Rocky”);

Singleton pattern: A Singleton is an object which can only be instantiated one time. Repeated calls to its constructor return the same instance and this way one can ensure that they don’t accidentally create multiple instances.

Example:

var object = new (function () {
this.name = “Rocky”;
})();

Que 6) What are some important features of JavaScript?

Some important features of JavaScript are as follows: