Because we still get questions about this in 2025, let’s clarify:

Back in the days, what people often called “JavaScript” in Unity was actually a language called UnityScript. It looked superficially similar to JavaScript, but under the hood, it was its own thing with different semantics and behaviors.

UnityScript was created specifically for Unity and was closer to ActionScript (used in Flash) than to ECMAScript-compliant JavaScript used in browsers and Node.js. It was compiled into .NET assemblies just like C#, and it worked alongside Boo and C# in the old days of Unity.

Eventually, Unity deprecated both UnityScript and Boo in favor of C#. So if anyone says “Unity used to support JavaScript,” link them this page or tell them:

“Nope, that was UnityScript, just a short-lived JavaScript lookalike.”