What is JavaScript? An introduction

JavaScript is one of the most popular and widely used programming languages in the world. If you have ever interacted with a website - clicked a button, watched an animation, filled in a form, or used a web app - you have almost certainly used JavaScript, even if you didn’t realise it.

At its core, JavaScript is a dynamically typed, asynchronous, interpreted language with Java-like syntax. Alongside HTML and CSS, it forms one of the three foundational technologies of the modern web. While HTML structures content and CSS controls how it looks, JavaScript brings pages to life by adding interactivity, movement and logic.

In practical terms, almost all interactivity on a webpage is powered by JavaScript. This central role is why JavaScript is often one of the first languages people choose to learn, and why it remains in such high demand.

If you’re considering whether JavaScript is right for you, StayAhead offers training in JavaScript and TypeScript to help you build skills with confidence.

A brief history of JavaScript

JavaScript was created in 1995 by Brendan Eich while he was working at Netscape Communications Corporation. At the time, the web was still in its early stages, and there was a growing need for a simple scripting language that could run directly in web browsers.

The language was originally called LiveScript, but it was soon renamed JavaScript as a strategic decision to align it with the popularity of Java at the time. Despite the similar names, Java and JavaScript are distinct languages with different purposes and designs. 

What JavaScript did achieve was something revolutionary: it made web pages interactive. That capability helped shape the web as we know it today.

What is JavaScript used for?

Given how widely JavaScript is used, it can sometimes feel like the answer to “what does JavaScript do?” is simply “everything”. While that might be an exaggeration, JavaScript’s versatility is one of its greatest strengths.

Originally developed to support interactive web pages, JavaScript is now used across many areas of software development, with web and application development its most popular function.

Web and mobile application development

JavaScript is the language behind most modern websites and web applications. It is also the foundation of popular front-end frameworks and libraries such as React, Angular, Vue and Svelte, which simplify the process of building complex, highly interactive applications.

Many of the world’s best-known platforms, including Netflix, Instagram, Facebook, WhatsApp and the BBC, rely on JavaScript frameworks like React. To work with any of these tools, a solid understanding of JavaScript is essential.

JavaScript is also widely used in mobile app development, allowing developers to reuse skills and logic across web and mobile platforms.

Back-end and server-side development

Although JavaScript is traditionally associated with the part of an application users see and interact with, it is increasingly used on the server side as well.

Thanks to runtimes such as Node.js, Deno and Bun, JavaScript can now handle back-end development tasks such as processing requests, working with databases and powering cloud-based services. This means developers can build both the front-end and back-end of an application using the same language, simplifying development and collaboration.

Other applications: VR and AI

JavaScript is also used in more emerging areas such as virtual reality and artificial intelligence. Technologies like WebXR allow JavaScript to interact with VR devices through the browser, while machine learning libraries such as TensorFlow.js build on JavaScript foundations to enable intelligent applications.

While these areas require more advanced knowledge, they highlight how far JavaScript has expanded beyond its original purpose.

What is TypeScript?

TypeScript is closely related to JavaScript and is increasingly mentioned alongside it in job descriptions and learning pathways. In simple terms, TypeScript builds on JavaScript by adding an extra layer of structure.

JavaScript is dynamically typed, meaning variables can change type as a program runs. This flexibility makes JavaScript easy to start with, but it can lead to unexpected errors in larger applications. TypeScript introduces static typing, allowing developers to catch certain mistakes earlier in development rather than at runtime.

As JavaScript is now used to build larger, more complex systems, TypeScript has grown in popularity as a way to improve reliability and maintainability. Many teams use both together, making TypeScript a valuable skill for JavaScript learners.

What makes JavaScript different from other programming languages?

JavaScript has several characteristics that set it apart.

Interpreted

Languages such as Java and C# typically require code to be manually compiled (converted into a form the computer can understand) before it can run. JavaScript does not. Instead, it is usually executed directly by a browser or runtime environment, making it quicker to test and iterate during development.

Dynamically typed

In JavaScript, a variable automatically takes on the type of data it is given, such as text or numbers. This makes the language flexible and approachable for beginners, though it can also introduce errors if not managed carefully, which is one reason TypeScript has become popular.

Event-driven

JavaScript was originally designed to respond to events such as mouse clicks, keyboard input or page loading. While it now does much more, this event-driven nature remains central to how interactive applications work.

DOM

The Document Object Model (DOM) represents a web page as a set of objects that JavaScript can interact with. By changing these objects, JavaScript can update content, styles and behaviour in real time. “DOM” simply describes how JavaScript connects logic to what users see on screen.

Asynchronous

JavaScript handles tasks such as loading data without blocking or pausing. This approach can take time to understand, but it allows applications to remain responsive and efficient, providing a major advantage for user experience.

Full-stack versatility

JavaScript can be used across the entire application stack. Developers can build front-end interfaces, back-end services and even shared logic using the same language and related tools.

Client-side and server-side

On the client side, JavaScript enhances interactivity and responsiveness in the browser. On the server side, it powers logic, data handling and APIs. This flexibility makes JavaScript especially attractive to learners aiming for full-stack development.

The advantages of JavaScript

JavaScript’s popularity is driven by its demand, versatility and relevance to modern development. It is an excellent choice if you want to become a web developer, work with frameworks such as React or Next.js, or move into full-stack development.

Like any language, it has challenges. Concepts such as asynchronous programming can take time to master, but these challenges are balanced by strong community support, extensive learning resources and wide industry adoption.

For learners willing to invest time and practice, JavaScript opens the door to a broad range of development roles.

To explore learning options, StayAhead offers flexible study routes for web development training, including virtual learning, classroom delivery and on-site programmes.

If you’re ready to take the next step or would like guidance on where to start, contact the StayAhead team.