What is JavaScript?

Learn everything you need to know about JavaScript, what it is used for, and why it is one of the main frameworks of front-end web development.

JavaScript, often abbreviated as JS, is a versatile programming language that plays a pivotal role in both frontend and backend development. At its core, it works seamlessly with HTML and CSS to structure and design web pages.

Although originally recognised for enhancing the interactivity of web pages with dynamic interactive features, it has evolved to power server-side applications as well. One notable example is Node.js, a JavaScript runtime that enables developers to build scalable and efficient backend systems.

Along with HTML and CSS, JavaScript stands out as one of the most commonly used programming languages. 98.4% of all websites use JavaScript as of March 2023.

In this guide from the experts at Propel Tech, we’ll cover everything JavaScript. You’ll learn the fundamental aspects, advantages, and applications of JavaScript. From understanding its core functionality to why it’s still one of the most valuable languages to learn.


Table of Contents


Understanding JavaScript

Understanding JavaScript

JavaScript was developed by Brendan Eich in 1995 while working for Netscape to help make early versions of the World Wide Web more dynamic. It quickly gained popularity as developers realised its ability to add dynamism and interactivity to web pages.

JavaScript is considered the Programming Language for the Web and core technology of the World Wide Web, alongside HTML and CSS. They work together to make the user-facing elements of most websites and online applications.

In the beginning, JavaScript was released alongside initial support for CSS and extensions to HTML:

  • HTML is the markup language that provides the basic layout, structure, and content of a website.
  • CSS gives design, fonts, colours, effects, and other visual elements to apply styling to HTML content.
  • JavaScript brings dynamism and interactivity to the website in the form of pop-ups, animations, video and social media embeds, drop-down menus, and many other website components.

These three layers build on top of one another, creating dynamic web pages and applications. JavaScript can calculate, manipulate and validate data. It can run directly in the browser, not just on a server, becoming one of the most commonly used programming languages on the internet.

The evolution of JavaScript

As the web developed from its basic form, so did the need for dynamic content. Initially named LiveScript, it quickly evolved to JavaScript. JS leveraged its synergy with Java, a prevalent programming language at the time.

This scripting language makes static web pages interactive, so developers can create engaging user experiences. The text uses simple words and short sentences to explain the language's benefits. The most important information comes first.

Standardisation through ECMAScript

Recognising the need for standardisation, Netscape submitted JavaScript to ECMA International in 1996. This collaboration birthed the ECMAScript standard in 1997, providing a universal framework for browser vendors to adhere to. JavaScript has been solidified as a language grounded in standards since ECMAScript 2 and up to the modern era. This ensured consistent execution across various browsers.

The advent of Node.js

In 2009, Node.js emerged as a groundbreaking development. This allowed JavaScript to transcend its traditional role confined to browsers. With the introduction of the Chrome V8 engine, Node.js enabled server-side development in JavaScript. This revolutionised the concept of full-stack development. Developers could now use JavaScript to write both client and server-side code.

JavaScript beyond the browser

As JavaScript continued to evolve, it transcended its initial boundaries. The introduction of AI/ML modules like Tensorflow.js showcased its adaptability. This made it a versatile language not only for web development but also for emerging technologies.

Frameworks, transpilers, and the future

JavaScript's journey includes the rise of frameworks like AngularJS, ReactJS, and the advent of transpilers. This has eased the challenges of browser compatibility. Today, JavaScript is not confined to websites alone. It powers mobile and desktop applications and serves as a backend server.

What is JavaScript used for?

What is JavaScript used for

JavaScript is versatile and can create a lot more than adding dynamism to web pages. The core client-side language consists of some common programming features that allow you to do things like:

  • Use variables to store valuable data
  • Perform operations on text segments, referred to as "strings". Strings are written inside quotes, either single or double
  • Execute code in response to specific events happening on a web page

Webpage interactions

JavaScript's capabilities extend far beyond static web content, enabling dynamic and interactive experiences. JavaScript excels in:

  • Event-driven programming
  • Capturing and processing user input
  • Manipulating the Document Object Model (DOM)
  • Handling asynchronous operations
  • Creating captivating animations

From responding to user actions to implementing transition effects, JavaScript empowers developers to craft engaging interfaces. Additionally, libraries and frameworks like jQuery, React.js, and Angular offer streamlined solutions, enhancing interactivity.

User Interfaces

Here are the key frameworks and libraries that have played pivotal roles in shaping user interfaces.

JavaScript Frameworks for User Interfaces


React.js has emerged as a powerhouse for building dynamic and responsive user interfaces. Developed and maintained by Facebook, React.js adopts a component-based architecture. It promotes reusability and maintainability. With its virtual DOM (Document Object Model) approach, React efficiently updates and renders components, ensuring optimal performance. The declarative syntax and unidirectional data flow contribute to a more predictable and efficient development process.


Angular is a robust front-end framework maintained by Google. It is known for its comprehensive feature set. Utilising TypeScript, Angular provides a structured approach to building scalable and modular user interfaces. Its two-way data binding and dependency injection mechanisms simplify complex application logic. Angular's CLI (Command Line Interface) streamlines project setup and maintenance, making it an excellent choice for large-scale applications.


For many years, jQuery stood as a fundamental library simplifying the complexities of JavaScript. Particularly in manipulating the DOM and handling events. While newer frameworks have emerged, jQuery remains relevant for its simplicity and cross-browser compatibility. It offers a concise syntax for common tasks, making it an accessible choice for developers aiming for quick and efficient UI development.

Application Programming Interfaces (APIs)

Application Programming Interfaces (APIs) are pre-built sets of code blocks that allow developers to implement programs that might be challenging or even impossible to develop otherwise. They generally fall into two categories:

Browser APIs

Browser APIs are integrated into your web browser and can expose data from the computer environment or perform complex and useful tasks. For instance:

  • The DOM (Document Object Model) API enables manipulation of HTML and CSS, allowing tasks like creating, removing, and modifying HTML elements, dynamically applying new styles to a page, and more. Every time you see a pop-up window displayed on a page is the DOM in action.
  • The Geolocation API retrieves geographical information, used in Google Maps, for example, to pinpoint your location and display it on a map.
  • The Canvas and WebGL APIs allow the creation of animated 2D and 3D graphics. Some projects using these web technologies can be explored on platforms such as Chrome Experiments and webglsamples.
  • Audio and Video APIs, such as HTMLMediaElement and WebRTC, offer interesting possibilities for multimedia applications. These APIs enable activities like playing audio and video directly on a web page or capturing video from your webcam and displaying it on another person's computer.

Third Party APIs

Third-party APIs are not built into the browser by default and usually need to obtain their code and information from somewhere on the web. For example, The Twitter API allows tasks such as showcasing the most recent tweets on your website. The Google Maps API and OpenStreetMap API allow embedding custom maps into your website.

How does JavaScript work?

JavaScript seamlessly integrates with HTML and CSS when loading a web page in a browser. It executes within a runtime environment (typically the browser tab). Unlike compiled languages, JavaScript is a runtime language, allowing it to be interpreted and executed on the fly as the browser processes the webpage.

JavaScript dynamically modifies HTML and CSS through the Document Object Model (DOM) API, enabling real-time updates to the user interface. This interaction between JavaScript and the DOM is what brings web pages to life, providing a dynamic and engaging user experience.

While HTML and CSS are primarily used for the front end, JavaScript's uniqueness lies in its ability to run directly in the browser, not confined to server-side execution. This distinction ensures that web pages remain dynamic and engaging, with JavaScript serving as the engine that powers interactive features directly within the user's browser environment.

Browser security

Every browser tab has its separate container for executing code, referred to technically as "execution environments." In most scenarios, the code in each tab runs independently, and the code in one tab cannot directly impact the code in another tab or on a different website. This serves as a crucial security measure. Without it, hackers could write code to steal information from other websites and engage in other harmful activities.

JavaScript running order

When the browser encounters a JavaScript block, it traditionally follows a procedural running order, executing the code sequentially from top to bottom. However, it's crucial to note that JavaScript, despite its procedural appearance, is inherently object-oriented in its nature, allowing for more dynamic and flexible execution patterns.

In an object-oriented context, JavaScript introduces the concept of functions, methods, and events, enabling a more modular and reusable approach to coding. Unlike strict top-to-bottom procedural languages, JavaScript allows for the definition of functions and objects, creating a structure where code can be executed based on events or function calls rather than a linear progression.

Interpreted versus compiled code

In interpreted languages, code is parsed at run time. There’s no need to transform the code into a different form before the browser runs it. The code is received in its original text form, which is programmer-friendly and is processed directly from there. This adds a layer that compiled code doesn’t have.

Compiled languages are transformed (compiled) into another form before they are executed by the computer. For example, languages like C/C++ are compiled into machine code, which is then run by the computer. The program is executed from a binary format, which was generated from the original program source code.

JavaScript is a lightweight-interpreted programming language. The web browser receives the JavaScript code in its original text form and executes the script accordingly. From a technical perspective, modern JavaScript interpreters use a technique called just-in-time compiling to boost performance. This involves compiling the JavaScript source code into a faster binary format while the script is in use.

Server-side versus client-side code

Client-side code refers to the code executed on the user's computer. When a web page is viewed, the client-side code of that page is downloaded, executed, and displayed by the browser.

Server-side code runs on the server, and its results are then downloaded and displayed in the browser. Common server-side web languages include PHP, Python, Ruby, ASP.NET and JavaScript.

What Sets JavaScript Apart?

JavaScript comes with several advantages that make it a top choice. The following highlights the benefits of using JavaScript.


JavaScript's straightforward structure makes it easy to learn, and implement, and also runs faster than other languages. Identifying and correcting errors is also a straightforward process.

Fast execution

JavaScript executes scripts directly in web browsers, removing the need to connect to a server first or rely on a separate compiler. Major browsers also support in-place compilation during program execution.


JavaScript seamlessly integrates with other languages like PHP, Perl, and Java through various interoperability mechanisms such as APIs and libraries. Developers often use JavaScript alongside PHP for client-side interactions and server-side processing.

Rich community support

With lots of resources and forums, JavaScript offers extensive support for beginners with limited technical expertise, fostering a collaborative learning environment. Backed by a dedicated development team and ECMA International, undergoes continuous updates. The creation of new frameworks and libraries ensures its ongoing relevance in the dynamic tech industry.

Reduced Server Load

Operating on the client side, JavaScript reduces server requests. Web browsers can handle data validation, and updates are limited to specific sections of web pages.

Final thoughts: what is JavaScript?

JavaScript stands as a versatile and dynamic programming language essential for web development. From its inception as a client-side scripting language to its expansion into server-side applications through platforms like Node.js, JavaScript has become a cornerstone in crafting interactive and responsive web experiences. Its ability to integrate with HTML and CSS has made it the most used programming language on the web.

As technology continues to evolve, JavaScript remains a powerful tool, driving the interactivity and functionality behind the web pages we see daily. Backed by a strong community of developers, JavaScript is easy to learn and implement into certain web page elements and remains compatible with many other languages.

JavaScript development at Propel Tech

php development at propel tech

At Propel Tech, we provide a wide range of software development services. We work across a range of technology stacks, and our expertise is tailored to meet diverse business needs.

From conceptualisation to deployment and ongoing maintenance, we offer end-to-end software development services. We ensure seamless experiences and high-quality outcomes.

Work with Propel Tech for software development.


Why do I need JavaScript enabled?

Lots of websites contain JavaScript to enable specific functionalities on web pages. Disabling JavaScript in your browser may result in limited or unavailable content and functionality on the webpage.

Is it difficult to learn JavaScript?

JavaScript is one of the most intuitive programming languages to learn and use; often, it’s one of the first that newbie developers learn when they start to code.

Is JavaScript still relevant?

Yes, as of 2024, JavaScript works as the backbone of web development, enabling the creation of interactive and dynamic websites and enhancing the user experience.

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