What is JavaScript? Complete Introduction

JavaScript is a lightweight, cross-platform, and interpreted compiled programming language which is also known as the scripting language for webpages.

What is JavaScript? Complete Introduction

JavaScript is a very powerful client-side scripting language. JavaScript is used mainly for enhancing the interaction of a user with the webpage. In other words, you can make your webpage more lively and interactive, with the help of JavaScript. JavaScript is also being used widely in game development and Mobile application development.  

An object-oriented, cross-platform programming language called JavaScript is used to create interactive websites (e.g., having complex animations, clickable buttons, popup menus, etc.). Additionally, there are more sophisticated server-side JavaScript variants, like Node.js, that enable you to enhance a website's functionality without having to download additional files (such as real-time collaboration between multiple computers). JavaScript can link to the objects of its environment inside a host environment (such as a web browser) and grant programmatic control over those objects. 

JavaScript contains a standard library of objects, such as Array, Date, and Math, and a core set of language elements such as operators, control structures, and statements. Core JavaScript can be extended for a variety of purposes by supplementing it with additional objects; for example:

  • Client-side By providing objects to manipulate a browser and its Document Object Model, JavaScript augments the fundamental language (DOM). Client-side extensions, for instance, enable an application to add elements to HTML forms and react to user actions like mouse clicks, form input, and page navigation.
  • Server-side JavaScript extends the core language by supplying objects relevant to running JavaScript on a server. For example, server-side extensions allow an application to communicate with a database, provide continuity of information from one invocation to another of the application, or perform file manipulations on a server.

This means that in the browser, JavaScript can change the way the webpage (DOM) looks. And, likewise, Node.js JavaScript on the server can respond to custom requests from code written in the browser.

A Brief JavaScript History

JavaScript was created at Netscape Communications by Brendan Eich in 1995. Netscape and Eich designed JavaScript as a scripting language for use with the company's flagship web browser, Netscape Navigator. Initially known as LiveScript, Netscape changed the name to JavaScript so they could position it as a companion for the Java language, a product of their partner, Sun Microsystems. Apart from some superficial syntactic similarities, though, JavaScript is in no way related to the Java programming language.

After its release, more and more browsers started adding JavaScript support. Still, for much of its history JavaScript was not regarded as a serious programming language. Its earliest releases suffered from notable performance and security issues, but developers had no alternatives. If they wanted to run programs in the browser, they had to use JavaScript.

In 2008, the creation of Google's open-source Chrome V8, a high-performance JavaScript engine, provided a crucial turning point for JavaScript. The subsequent proliferation of fast JavaScript engines made it possible for developers to build sophisticated browser-based applications with performance that competed with desktop and mobile applications.

Soon after, Ryan Dahl released an open-source, cross-platform environment called Node.js. It provided a way to run JavaScript code from outside a browser. It freed JavaScript from the browser's confines and led directly to JavaScript's current popularity. Today, you can use JavaScript to write all kinds of applications, including browser, server, mobile, and desktop applications. Most major online companies today, including Facebook, Twitter, Netflix, and Google, all use JavaScript in their products. 

Javascript Features 

JavaScript is one of the most popular languages which includes numerous features when it comes to web development. It's amongst the top programming languages as per Github and we must know the features of JavaScript properly to understand what it is capable of. 

Some of the features are lightweight, dynamic, functional, and interpreted. Now we are going to discuss some important features of JavaScript.

  • Light Weight Scripting language

  • Dynamic Typing

  • Object-oriented programming support

  • Functional Style

  • Platform Independent

  • Prototype-based

  • Interpreted Language

  • Async Processing

  • Client-Side Validation

  • More control in the browser

Let's see all of these features in detail so that you can understand them. Some of the above-specified features are old JavaScript features while some of them are new features.

1. Light-Weight Scripting Language

JavaScript is a lightweight scripting language because it is made for data handling at the browser only. Since it is not a general-purpose language so it has a limited set of libraries. Also as it is only meant for client-side execution and that too for web applications, hence the lightweight nature of JavaScript is a great feature.

2. Dynamic Typing

JavaScript supports dynamic typing which means types of the variable are defined based on the stored value. For example, if you declare a variable x then you can store either a string or a Number type value or an array or an object. This is known as dynamic typing.

To illustrate this, consider the difference between defining a variable in JavaScript and declaring a variable in a language like Java where we must specify the data type explicitly. To declare a variable in JavaScript, we only need to use the var or let keyword before the variable name without bothering about its type.

3. Object-Oriented Programming Support

Starting from ES6, the concept of class and OOPs has been more refined. Also, in JavaScript, two important principles with OOP in JavaScript are Object Creation patterns (Encapsulation) and Code Reuse patterns (Inheritance). Although JavaScript developers rarely use this feature but is there for everyone to explore.

3. Functional Style

This suggests that JavaScript adopts a functional approach since even objects are produced from constructor functions, each of which denotes a specific sort of object. In JavaScript, functions can also be passed to other functions and used like objects.

4. Platform Independent

This implies that JavaScript is platform-independent or we can say it is portable; which simply means that you can simply write the script once and run it anywhere and anytime. In general, you can write your JavaScript applications and run them on any platform or any browser without affecting the output of the Script.

5. Prototype-based Language

JavaScript is a prototype-based scripting Language. This means javascript uses prototypes instead of classes or inheritance. In languages like Java, we create a class and then we create objects for those classes. But in JavaScript, we define an object prototype and then more objects can be created using this object prototype.

7. Interpreted Language

Because JavaScript is an interpreted language, each line of the script that is written in it is read and executed. A JavaScript interpreter, which is a built-in feature of the Web browser, interprets these scripts. However, many JavaScript engines today use just-in-time compilation for JavaScript code, including the V8 engine in Chrome.

8. Async Processing

JavaScript supports Promise which enables asynchronous requests wherein a request is initiated and JavaScript doesn't have to wait for the response, which at times blocks the request processing. Also starting from ES8, Async functions are also supported in JavaScript, these functions don't execute one by one, rather they are processed parallelly which has a positive effect on the processing time, reducing it to a great extent.

9. Client-side Validations

This is a feature that is available in JavaScript forever and is still widely used because every website has a form in which users enter values, and to make sure that users enter the correct value, we must put proper validations in place, both on the client side and on the server-side. JavaScript is used for implementing client-side validations.

10. More control in Browser

Due to the fact that JavaScript is a client-side language, it offers a number of features that assist developers in splitting processing between the browser and the server, thereby reducing the load on servers by having fundamental processing, validations, temporary data saving using cookies, etc. on the browser itself.

Along with all these features, JavaScript provides the following useful features too:

  • Detecting browser type, name OS version, etc information of the client for analysis.

  • Extensive in-built library with many useful functions for validation, data type conversion, string operations, etc.

  • It is an object-centered language with Window Object being the most important object in JavaScript and it also supports Polymorphism.

  • Support for commonly used complex data types like array, Maps, List, etc. with support of in-built functions to operate on them.   

Applications of JavaScript

JavaScript is widely used for building websites and web applications. Let’s discuss some practical applications of JavaScript in various segments.

1. Web Development

Web pages are created using the scripting language JavaScript. JS, which was created in Netscape, enables programmers to create dynamic and interactive web pages that interact with users and carry out complicated actions. Additionally, it allows users to insert material into a document without refreshing the page. For validation and to support external applications like PDF files, widgets, and flash programs, the majority of websites employ JavaScript. The user experience is enhanced by JavaScript in some of the biggest tech companies in the world.

Some famous websites built by the use of JavaScript are Google, YouTube, Facebook, Wikipedia, Yahoo, Amazon, eBay, Twitter, and LinkedIn, to name a few. 

2. Web Applications

Various JavaScript frameworks are used for developing and building robust web applications. In an application like Google Maps, if users want to explore a map, all they have to do is click and drag the mouse to get a detailed view. JavaScript, which interacts with the browser without contacting the servers, powers this. React Native, React, Angular, and Vue are popular JavaScript front-end frameworks that aid in the development of online applications. Application Programming Interfaces and the AngularJS JavaScript framework were used in the development of Netflix and PayPal (APIs).

3. Presentations

A very popular application of JavaScript is to create interactive presentations as websites. The RevealJs and BespokeJs libraries can be used to generate web-based slide decks using HTML. With transitional styles, themes, and slide backgrounds in all CSS color formats, the RevealJs makes it easier to construct interactive slide decks. Scaling, animated bullet lists, syntax highlighting, and other features may be found in the feature-rich framework known as BespokeJs. Users can create presentations like webpages using JavaScript even if they are not completely versed in a programming language.

4. Server Applications

JavaScript is also used to write server-side software through Node.js open-source runtime environment. Developers can write, test and debug code for fast and scalable network applications. JavaScript helps to generate content and manage HTTP requests. Top companies like Walmart, PayPal, Uber, GoDaddy, and many more have adopted Node.js for server infrastructure. 

5. Web Servers

Node.js allows developers to use JavaScript to create a web server. Node.js being event-driven, it moves to the next call without waiting for the response of the previous call. The servers quickly transfer chunks of data without buffering. The HTTP module uses the createServer () method for creating a server. 

6. Games

Creating games on the web is another important one among applications of JavaScript. The combination of JavaScript and HTML5 plays a major role in game development using JS. The EaselJS library provides rich graphics for games. HTML5 provides total access to the web without additional plugins like Flash. Complex browser games Tower Building, CrossCode, and HexGL game are based on JavaScript and HTML5.  

7. Art

A recent feature of HTML5 in JavaScript is the canvas element, which allows drawing 2D and 3D graphics easily on a web page. This has helped open doors for various digital art projects on the browser. Become a digital artist, creating your own code of art using JavaScript.

8. Smartwatch Apps

Pebble.js is a JavaScript framework by Pebble, allowing developers to create applications for Pebble watches using JavaScript. Create a smartwatch app with simple JavaScript code. 

9. Mobile Apps

One of the most powerful applications of JavaScript is to create apps for non-web contexts, meaning for things, not on the Internet. With the use of mobile devices at an all-time high, JavaScript frameworks have been designed to facilitate mobile app development across various platforms like IOS, Android, and Windows. React Native framework allows cross-platform mobile app building, where developers can use a universal front end for Android and IOS platforms.

10. Flying Robots

Last but not least, you can use JavaScript to program a flying robot. With the Node.js ecosystem, users can control numerous small robots, creative maker projects, and IoT devices. Step into the exciting world of drones, flying robots, and quadcopters with JavaScript.      

Nearly every computing device that we use today has the use of JavaScript – iPhones, Androids, Mac OS, Windows, Linux, and Smart TVs. The significant reasons why JavaScript became universally adopted for web development include:

  • It can be used both in the front-end and back-end of web development
  • Serves everyone from beginners to intermediate and even advanced developers
  • Can run on all devices
  • It does not need an environment setup
  • Standardized and gets frequently updated with new versions
  • Open Standards and Community
  • Works with Document Object Model (DOM) for response to user interactions
  • Transformed web browsers into application platforms
  • Wide range of frameworks and libraries to help build complex applications  

Why JavaScript is known as a lightweight programming language?

JavaScript is considered lightweight due to the fact that it has low CPU usage, is easy to implement, and has a minimalist syntax. Minimalist syntax as in, it has no data types. Everything is treated here as an object. It is very easy to learn because its syntax is similar to C++ and Java.

A lightweight language does not consume much of your CPU’s resources. It doesn’t put excess strain on your CPU or RAM. JavaScript runs in the browser even though it has complex paradigms and logic which means it uses fewer resources than other languages. For example, NodeJs, a variation of JavaScript not only performs faster computations but also uses fewer resources than its counterparts such as Dart or Java.

Additionally, when compared with other programming languages, it has fewer in-built libraries or frameworks, contributing to another reason for it being lightweight. However, this brings a drawback that we need to incorporate external libraries and frameworks. 

Is JavaScript compiled or interpreted or both?

Both JavaScript is compiled and is also interpreted. The only interpreter used in earlier iterations of JavaScript was one that ran code line by line and displayed the outcome instantly. But as time went on, the performance started to be a problem because of the delayed interpretation. Therefore, the JIT compiler was also included in later versions of JS, possibly after V8, to optimize the execution and display the output more quickly. The bytecode produced by this JIT compiler is comparatively simpler to code. These instructions in this bytecode have been extensively optimized.

The V8 engine initially uses an interpreter, to interpret the code. On further executions, the V8 engine finds patterns such as frequently executed functions, and frequently used variables, and compiles them to improve performance.

What makes JavaScript unique?

There are at least three great things about JavaScript:

  • Full integration with HTML/CSS.
  • Simple things are done simply.
  • Supported by all major browsers and enabled by default.

JavaScript is the only browser technology that combines these three things.

That’s what makes JavaScript unique. That’s why it’s the most widespread tool for creating browser interfaces.

That said, JavaScript can be used to create servers, mobile applications, etc. 


  • JavaScript is a client-side scripting language developed by Brendan Eich.
  • JavaScript can be run on any operating system and almost all web browsers.
  • You need a text editor to write JavaScript code and a browser to display your web page. 
  • JavaScript was initially created as a browser-only language, but it is now used in many other environments as well.
  • Today, JavaScript has a unique position as the most widely-adopted browser language, fully integrated with HTML/CSS.
  • There are many languages that get “transpiled” to JavaScript and provide certain features. It is recommended to take a look at them, at least briefly, after mastering JavaScript.