What is JavaScript? The language that outgrew the browser

A language built to bring web pages to life

When you click a button on a web page and something changes without the page reloading, that’s usually JavaScript at work. On its main MDN page, it’s defined as “a lightweight interpreted (or just-in-time compiled) programming language with first-class functions”: dynamically typed, built on prototypes rather than classical classes, with automatic garbage collection, and able to work across several paradigms — imperative, functional, object-oriented. It’s best known as the scripting language of web pages, the one that manipulates page content (the DOM) inside the browser, responds to clicks and other events, fetches data from a server with the fetch() API, draws with canvas, and talks to the device through a range of other APIs, as MDN’s glossary explains. To see how the web got here, it helps to trace how the internet changed from a network of static pages into something interactive.

A taste of the syntax

You don’t need to know how to code to recognize JavaScript when you see it: a variable and a function, small algorithms you can call by name, are enough.

Practical example: a minimal snippet that defines and uses a variable might look like this:

let name = "Recaplica";
function greet(who) {
  console.log(`Hello, ${who}!`);
}
greet(name);

In the browser, these lines can run in the developer tools console and print “Hello, Recaplica!” into the open page. With Node.js, the same file also runs from the command line, with no browser open at all: it’s the same distinction described for PHP, between a language that only lives in the browser and one that can live outside it too.

From Netscape’s beta to the ECMAScript standard

JavaScript was born in 1995: Brendan Eich wrote it for Netscape, and its first public appearance dates to December 4, 1995. In the Netscape Navigator beta of September 1995 it was still called “LiveScript”; the name was changed to “JavaScript” only for the official release in December, right in the middle of the Java boom during the dot-com bubble. Eich himself, according to multiple web-history sources, called that choice “a marketing ploy by Netscape.”

From ES6 onward, the standard gets a new edition every year: in the words of MDN’s glossary, it’s “a living standard,” maintained by the TC39 technical committee at Ecma International, while the related Web APIs stay under W3C and WHATWG. A legend common in web history says the language’s first prototype, called “Mocha” according to some secondary sources, came together in about 10 days in May 1995, under pressure from a demo tied to the Netscape-Sun agreement on Java. Other web-history sources point out that this is a simplification: the initial prototype was written quickly, but the language was then refined over the following months, up to the December release. The one solid fact, confirmed by multiple independent sources, is the language’s birth in 1995 at Netscape, by Brendan Eich’s hand.

Outside the browser: Node.js and the rest of the ecosystem

For almost fifteen years, JavaScript stayed a nearly browser-only language. Things changed in 2009, when Ryan Dahl released Node.js on May 27, criticizing how badly traditional servers handled thousands of simultaneous connections under a sequential programming model. Node.js combines Google’s V8 engine — the same one that powers Chrome, made open source in September 2008 — with an event loop and a low-level, non-blocking input/output API: Node.js’s official site describes it as “an asynchronous event-driven JavaScript runtime, designed to build scalable network applications,” built without a thread-based model, even though it can take advantage of multi-core processors through child processes and the cluster module. Dahl presented the project on November 8, 2009, at the first European edition of JSConf; in January 2010, npm arrived, the package manager that made installing and distributing code written for Node.js much easier.

Libraries have grown up on top of this ecosystem: React, for instance, started as a prototype in 2011, built by Jordan Walke, an engineer at Facebook, and went open source on May 29, 2013, during the JSConf conference. As of 2026, Meta maintains it together with a community of independent developers, under the MIT open-source license.

The most common misunderstanding: JavaScript is not Java

The name has caused confusion for years: MDN dedicates an explicit note to clarifying that JavaScript shouldn’t be confused with the Java language, and that it’s not “interpreted Java.” The two languages, as Wikipedia also puts it, “are distinct and differ greatly in design,” despite sounding alike and sharing part of their syntax. Both trademarks, “Java” and “JavaScript,” belong to Oracle in the United States and other countries — but they remain two separate technologies, built for different purposes.

The most used language, by the numbers

According to the 2025 Stack Overflow Developer Survey, JavaScript is the single most used programming language: 66% of respondents to the technology section report using it, out of a base of 31,771 people. HTML/CSS follows at 61.9%, then SQL at 58.6% and Python at 57.9%. Python grew by 7 percentage points from 2024 to 2025, driven by artificial intelligence and data science, but in the 2025 edition of the survey JavaScript still comes out as the most widely used language among people who write software.