What is JavaScript?

JavaScript is one of the most popular programming languages today. It was created in 1995 by Brendan Eich (in just 10 days!) to be a programming language that runs in your browser. It’s the only programming language that runs natively in every web browser. That’s why it became so dominant.

JavaScript is what makes web pages interactive. It’s what lets you click buttons, fill out forms, see animations, and interact with websites without the page refreshing. When you visit a website, your browser downloads three main things: HTML for the structure, CSS for the styling, and JavaScript for the behavior.

For the first 15 years or so, JavaScript only ran in browsers. Then in 2009, [Node.js](/questions/A05S6q/what-is-nodejs) came along and let you run JavaScript on servers too. This was huge because developers could now use the same language for both frontend and backend. That’s part of why JavaScript exploded in popularity.

Today, JavaScript is everywhere. It powers interactive websites, mobile apps (through frameworks like React Native), and desktop apps (through Electron). It’s consistently one of the most popular programming languages in the world.

The language itself has evolved a lot. Modern JavaScript (often called ES6 or later) is much more powerful than the early versions. You’ll see JavaScript in frameworks like React, Vue, and Angular, and in server frameworks like Express and NestJS.

I started learning JavaScript in the early 2000s when it was mostly used for simple things like image rollovers and form validation. It’s come a long way since then. Now you can build entire applications with just JavaScript. In one way or another, I’ve used JavaScript at every professional job I’ve ever had and on every side project.