What is JavaScript?
JavaScript is a dynamically-typed scripting language that runs natively in every web browser, making it the language of client-side interactivity on the web. It has also become widely used on servers (via Node.js), in mobile apps, and even for CLI tools, largely because of its single-language reach across the whole stack.
Example
document.querySelector("button").addEventListener("click", handler) wires up a click event.
Related tool
Try it on ToolSphere — runs entirely in your browser, nothing is uploaded to a server.