Javascript Tutorial


JavaScript, often abbreviated as JS, is a programming language that conforms to the ECMAScript specification. JavaScript is high-level, often just-in-time compiled, and multi-paradigm. It has curly-bracket syntax, dynamic typing, prototype-based object-orientation, and first-class functions.

JavaScript is a text-based programming language used both on the client-side and server-side that allows you to make web pages interactive. Where HTML and CSS are languages that give structure and style to web pages, JavaScript gives web pages interactive elements that engage a user.


JavaScript is a scripting or programming language that allows you to implement complex features on web pages — every time a web page does more than just sit there and display static information for you to look at — displaying timely content updates, interactive maps, animated 2D/3D graphics, scrolling video jukeboxes

How does JavaScipt work?

JavaScript is what is known as a client-side script. Most Web applications, such as a search engine work because of an interaction between the user’s device (e.g. computer, phone or tablet and a remote server. The software on the remote server sends information to the client (i.e. the user’s machine) and the software on the client side reads the information and renders a Web page on screen.

A client-side script is a programming language that performs its tasks entirely on the client’s machine and does not need to interact with the server to function. For instance, if you have a Web page loaded on your computer and your Internet service provider goes down, you are still able to interact with the Web pages already loaded on your browser. You will not, however, be able to navigate to new Web pages or access any data located remotely.

Some of the dynamic website enhancements performed by JavaScript are:

  • Autocomplete
  • Loading new content or data onto the page without reloading the page
  • Rollover effects and dropdown menus
  • Animating page elements such as fading, resizing or relocating
  • Playing audio and video
  • Validating input from Web forms
  • Repairing browser compatibility issues

While JavaScript is a client-side language, some of its most powerful features involve asynchronous interaction with a remote server. Asynchronous simply means that JavaScript is able to communicate with the server in the background without interrupting the user interaction taking place in the foreground.

Take a search engine for example. Today, search engines almost all have an autocomplete function. The user begins typing a word into the search box and a list of possible search terms or phrases appears below. The experience is seamless. Suggested search terms appear without reloading the page.

In the background, JavaScript reads the letters as the user types, sends those letters to a remote server and the server sends suggestions back.

The software on the server side analyzes the words and runs algorithms to anticipate the user’s search term. Such programs are diabolically large and complex. The JavaScript on the client’s machine is as simple and small as possible so as not to slow down the user’s interaction. The communication between JavaScript and the server-side program is limited by the user’s bandwidth. This is why developers prioritize efficiency in JavaScript functions and make the amount of data communicated between the programs as small as possible.

Only once the user selects a search term does the entire page reload and produce the search results. Engines such as Google have reduced or eliminated the need to reload, even for that step. They simply produce results using the same asynchronous process.


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 understand this, in languages like Java, we explicitly mention that a particular variable will store a certain type of data, whereas in JavaScript we do not have to provide the data type while declaring a variable. In JavaScript, we just have to use var or let keyword before the variable name to declare a variable without worrying 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 its there for everyone to explore.

3. Functional Style

This implies that JavaScript uses a functional approach, even objects are created from the constructor functions and each constructor function represents a unique object-type. Also, functions in JavaScript can be used as objects and can be passed to other functions too.

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 object prototype and then more objects can be created using this object prototype.

7. Interpreted Language

JavaScript is an interpreted language which means the script written inside javascript is processed line by line. These Scripts are interpreted by JavaScript interpreter which is a built-in component of the Web browser. But these days many JavaScript engines in browsers like the V8 engine in chrome uses just in time compilation for JavaScript code.

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 which is available in JavaScript since 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

JavaScript being a client-side language provides many features that help developers to divide processing between browser and server hence reducing the load on servers by having basic 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.


The importance of JavaScript as a web technology can be determined from the fact that it is currently used by 94.5% of all websites. As a client-side programming language, JavaScript helps web developers to make web pages dynamic and interactive by implementing custom client-side scripts. At the same time, the developers can also use cross-platform runtime engines like Node.js to write server-side code in JavaScript. They can even combine JavaScript, HTML5 and CSS3 to create web pages that look good across browsers, platforms, and devices. There are also a number of reasons why each modern web developer must know how to leverage all benefits of JavaScript.

Why No Web Developer can Create Modern Web Applications without JavaScript?

Implement Client-Side Scripts

JavaScript was originally designed as a client-side scripting language. A large percentage of websites still use JavaScript as a client-side programming language. The web developers can easily write custom client-side scripts in JavaScript, and integrate the scripts seamlessly into HTML. They can further use JavaScript to make the web pages interactive, respond to users instaneously, and create richer user interfaces, without less server interaction and reduces server load.

Write Server-Side Code

The web developers can also write server-side code in JavaScript by using a cross-platform runtime engine like Node.js. Node.js is designed as a cross-platform and server-side runtime environment. It further executes the JavaScript code efficiently through Google V8 JavaScript engine. The built-in libraries provided by Node.js further allow programmers to run their web applications smoothly without relying on external web servers. Hence, the web developers can use Node.js to write both client-side and server-side code in JavaScript.

Simplify Complex Web Application Development

Despite being an interpreted programming language, JavaScript simplifies development of complex web applications by allowing developers to simplify the application’s composition. The programmers can use JavaScript libraries to create shadow DOM boundaries. In addition to simplifying the web application’s structure, the shadow DOM further decouples components of individual JavaScript libraries. The shadow DOM further make web browsers deliver documents with widely used HTML tags like div, select and input.

MEAN Stack

The developers can further simplify development of modern web applications by taking advantage of four components of MEAN stack — MangoDB, Express.js, Angular.js and Node.js. MangoDB is a modern and schemaless NoSQL database, whereas Angular.js is a popular JavaScript framework supported by Google. At the same time, Node.js is a cross-platform and server-side runtime environment, whereas Express.js is designed with features to simplify development of single-page and multiple-pages websites. The four components of MEAN stack enable developers to write both front-end and back-end of a website in JavaScript. However, components of MEAN stack are still interoperable.

Responsive Web Design

Most developers nowadays adopt responsive web design to make a website accessible and look good across multiple browsers, devices and browsers. Responsive web design enables developers to optimize a website for both computers and mobile devices with a single code base. But the developers have to combine CSS3, HTML5 and JavaScript to make the web pages responsive. Hence, the developers must use JavaScript to optimize web pages for mobile devices.

Google AMP Project

Google has initiated the Accelerated Mobile Pages (AMP) project to create websites that deliver richer user experience across varying mobile devices. Google has combined several optimization techniques to increase the loading speed of mobile web pages directly. But it requires developers to integrate AMP technology into the web pages through HTML5, CSS3 and JavaScript. Hence, the programmers have to use JavaScript while optimizing websites for mobile devices with AMP.

Many Transpilers

JavaScript is a lightweight programming language. It lacks some of the robust features provided by modern programming languages like Java and C#. But the web developers can easily extend JavaScript by using a transpilers like CoffeeScript, TypeScript, DukeScript and Vaadin. Each transpiler enables developers to meet the requirements of large enterprise application by making the workflow complex.

Varying Libraries and Frameworks

The web developers can easily extend the functionality of JavaScript by using a number of libraries and frameworks. The fully-features JavaScript libraries like AngularJS and Ember enable JavaScript web developers to add functionality to complex web applications without writing additional code. At the same time, lightweight JavaScript libraries like React.js make it easier for programmers to accomplish specific tasks. The developers can further use open source tools like NPM to install and manage all JavaScript libraries used by a web application efficiently.

Keeps Evolving

As mentioned earlier, JavaScript lacks some of the advanced features provided by modern programming languages like multithreading capability and file read/write option. But the programming language has been evolving consistently to meet the emerging trends in web application development. For instance, ECMAScript 6, the latest version of JavaScript simplifies modern web application development by providing several new classes, modules, module loaders, generators and symbols, along with Unicode support and reflect API.

The modern web developers must use JavaScript to make their web applications deliver optimal user experience across various devices, operating systems, and browsers. However, they must be familiar with various JavaScript libraries, frameworks, and tools. They can even combine multiple libraries and frameworks to enhance and extend JavaScript according to requirements of large projects.

Top 10 Places to Learn JavaScript Online

Here is my curated list of six websites to learn JavaScript online for FREE. It includes interactive websites, official resources, good books, and other resources.

1. Introduction to JavaScript @ Codecademy

In one word, this is one of the best free JavaScript tutorials, and I have learned JavaScript from this website. It is also one of the best platforms to learn new technologies online but probably the best website to learn JavaScript online.

Even though currently, Codecademy offers JavaGitUNIX command line, and several other courses, it made its name by an interactive JavaScript course to learn online at your own pace.

You can gauge the popularity of this course by looking at the number of students enrolled, currently, 5M+, which is a very high number for any online FREE course.

You can sign up for this free JavaScript tutorial here.

In short, Codecademy is one of the best websites to learn JavaScript online, and you should take advantage of this.

2. Free JavaScript Tutorials @ Udemy

This is one of the best places for online learning. You will get free online courses and tutorials in all the latest technology and programming language like JavaSpringData Structure and Algorithms, Selenium, REST, etc. It provides both free and paid resources.

Here is a couple of useful courses and JavaScript tutorials to learn some of the interesting technologies:

  1. The Complete JavaScript Course 2021: Build Real Projects! (link)
  2. The Web Developer Bootcamp (link)
  3. JavaScript Bootcamp — Build Real World Applications (link)
  4. Javascript Essentials (FREE)(link)

The paid resources are also very cheap, and you can purchase on just $9.99 during their flash sale, which happens quite often. It’s full of some of the great teachers like Colt_SteeleRob PercivalStephen GriderJose Marcial Portilla, John Purcell, etc.


3. JavaScript Guide @

This is one of the most awesome community websites which will help you to learn to code for free, build real-world projects, and get a job as a developer.

It has a massive collection of interactive tutorials and exercises to learn JavaScriptData Structure and AlgorithmsFrontend Development, and so on.

Founded by Quincy Larson, this is a really excellent place to start your coding journey. They even have a big Facebook group (freecodecampearth) where you can ask questions and share your learning experience, and their Medium publication freeCodeCamp is the most significant Medium publication for Programming articles.

As Quincy Larson pointed out in comments, freeCodeCamp also has a YouTube channel, which has hundreds of free courses on topics like Python, Git, GraphQL, SQL, database schema design, and a lot of advanced topics. Many of these are 10+ hours long — in a single video with no ads. Perfect to start your journey.


4. Programming Foundations with JavaScript, HTML, and CSS @ Coursera

This is another awesome website to learn online, which has lots of free JavaScript tutorials and courses. It’ founded by Stanford professors Andrew Ng and Daphne Koller, and it offers courses, specializations, and online degrees.

The best part of Coursera is that it offers online courses from Universities like Stanford, University of London, University of Michigan, Colorado, Imperial College of London, and many more.

It provides both free and paid online courses and specialization. Some of my favorite free JavaScript courses and tutorials from Coursera are :

  1. Programming Foundations with JavaScript, HTML and CSS (link)
  2. HTML, CSS, and Javascript for Web Developers (link)
  3. Interactivity with JavaScript (link)

Coursera also provides you Certification, which you can showcase in your Linkedin profile, but you need to pay for it.

And, if you find Coursera courses useful, which they are because they are created by reputed companies like GoogleIBMAmazon, and best universities around the world, I suggest you join the Coursera Plus, a subscription plan from Coursera

This single subscription gives you unlimited access to their most popular coursesspecialization, professional certificate, and guided projects. It cost around $399/year but its complete worth of your money as you get unlimited certificates.

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5. JavaScript 30

This is one of the best websites to learn JavaScript for free. It contains a lot of free JavaScript tutorials and lessons. Created by Wes Bos, this is a great free resource for JavaScript developers. Check out JavaScript 30 to up your JavaScript game with fun little projects.

Some of the highlights of my favorite free JavaScript tutorial is :

30 Day Vanilla JS Coding Challenge

Build 30 things in 30 days with 30 tutorials

No Frameworks×No Compilers×No Libraries×No BoilerplateJavaScript 30Build 30 things with vanilla JS in 30 days with 30

6. Pluralsight JavaScript courses

One of the best websites to learn any technology, skills like Web Development, Mobile Development, and Programming language like Java, Web development framework like AngularReactSpring FrameworkHibernate, etc.

The site also has a lot of useful courses to learn JavaScript from beginners perspective like :

  1. JavaScript Fundamentals By Liam McLennan
  2. JavaScript From Scratch By Jesse Liberty
  3. Basics of Programming with JavaScript By Kyle Simpson

It’s also now acquired CodeSchool, which earlier allows you to learn web technologies by doing it. I use this website to learn a lot of cool stuff in no time.

By the way, you would need a Pluralsight membership to join this course which costs around $29 per month and $299 per annum (14% discount) but its completely worth it. Alternative. you can also use their 10-day-free-trial to watch this course FREE.


7. JavaScript tutorials on Mozilla Developer Network

Mozilla is a serious learner, a programmer who loves to do their own thing and just wants to read the theory and try examples in their own setup.

Unlike Codecademy and The Educative Team, this is not interactive, but you will find detailed information. Mozilla is also the official source for any JavaScript information.

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I use this site as reference documentation for many JavaScript, it contains a wealth of information, and you can do the same too.

8. Katas @ Code Combat

JavaScript can be a reasonably easy way to add added functionality to your web page, but learning JavaScript on your own can be a daunting task. CodeCombat is a platform for students to learn computer science while playing through a real game.

Courses have been specifically playtested to excel in the classroom, even by teachers with little to no prior programming experience. It has some web development courses to learn the basics of JavaScript.

In short, a website more suitable for beginners and students. You can learn the basics of JavaScript fairly quickly by following their unique style.

9. Learn JavaScript Online — CodeMentor

Another great site which provides interactive JavaScript tutorial. This website offers a 4-week course to learn JavaScript, in fact, to master JavaScript, as the course claims. You will not only learn about core JavaScript but also about other famous JavaScript libraries and related concepts


That’s all about these best websites to learn JavaScript online. If you are serious about learning JavaScript, then you must not just sit back and relax but also start developing some real-world projects, start using popular JavaScript libraries like jQueryAngularReact, and Node JS to become proficient on what industry is expecting from a JavaScript Developer.

If you like to read books more than websites, then you also start with reading Head First JavaScript, one of the best books to learn JavaScript from scratch.

Head First JavaScript,

10. Introduction to JavaScript: First Steps by The Educative Team

If you don’t know, Educative is another online learning platform that is gaining a lot of traction for its text-based, interactive learning courses. Reading is generally faster than watching, and If you prefer reading text than watching videos, then this is the platform to checkout.

It has some of the best courses to prepare for coding interviews like Grokking the Coding Interview: Patterns for Coding Questions and Grokking the system design interview.Grokking the System Design InterviewSystem design questions have become a standard part of the software engineering interview process. Performance in these…

It also has a lot of free resources like this free JavaScript tutorial to learn essential technologies. You can register for this course for free, but if you like to take full advantage of the platform, I suggest you buy its membership, which costs $17(50% discount now) monthly, completely worth it for a programmer and software engineers where continuous learning is required.

This is an introduction to JavaScript for the complete beginner. It’ll provide the fundamentals of the language. Topics include variables, operators, functions, arrays, objects, and loops. After this course, you should be ready to further your learning through advanced classes or other resources. There is NO installation required for this course.

The code can be viewed and run directly from the lessons. This course has been created by Arnav Agarwal, a full-stack engineer. Arnav has attended a coding boot camp and has taught at another one.

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