JavaScript

PowerUI presently runs Javascript via Jint and an implementation of WebAssembly. It previously included a series of custom Javascript engines which were fast but ultimately fell short when it came to standards compliance.

The JavaScript challenge - A short history

Most gaming platforms, including iOS, explicitly don't allow runtime compliation. JavaScript was designed to be runtime compiled so these restrictions cause an instant major problem. It's not like it's a particularly small issue either - all but two of the Unity platforms (Standalone and Android) don't allow runtime compilation. The only route to get JavaScript working on those platforms is to compile the JavaScript 'ahead of time' in the editor. However, that is extremely difficult for a language as dynamic as JavaScript is. We initially went the same route as Unity - create a JavaScript-like language which can be easily compiled in the editor. That was Nitro.

If you've ever used UnityScript (or Nitro itself) you will notice very quickly that you can't simply run a library like jQuery, or indeed virtually any actual JavaScript from the web (it's still very unfortunate that Unity still calls UnityScript 'JavaScript' and uses the .js extension). So over the years as PowerUI's support for the web in general has increased, we naturally needed to make a new JavaScript engine - one which supported ahead of time compilation and as much of the JavaScript specification as possible. That's Nitrassic.

Nitrassic was built by taking the Jurassic engine and merging it with Nitro (thus the name) - adding a type tracking system to make it suitable for editor compilation. This ultimately had the effect of making Jurassic massively faster, but at the expense of months of high complexity compiler work. We're in new territory here - Nitrassic is the first ahead-of-time JavaScript compiler which could have big implications for things like Node.js in the wider web world; particularly as, when combined with IL2CPP, the result is JavaScript running at near native speeds.

Since then however, running Javascript has become a little easier so presently PowerUI runs Jint for full standards compliance.

Can I run x - How compliant is the JavaScript in PowerUI?

The best option? Just try it and see what happens! At the moment, this depends on the Web API's that you intend to use. PowerUI currently has broad support for a variety of web APIs. The API coverage is enough such that jQuery and basic React works for example.

Interaction with the rest of your code

Running Javascript is a little useless if you can't make it interact with your game, and vice versa. Here's how to get that going.

Calling C#/Unity methods from JS

You'll need the classes you want to use to be inside a namespace. From there, you can then import the namespace like this:

// You can use the Unity API directly too:
var UnityEngine = importNamespace("UnityEngine");

var go = new UnityEngine.GameObject();

go.name = "MadeWithLoveByRealJavaScript";

Calling JS from C#

To call JS functions from C#, use document.Run:

var document = UI.document;
document.Run("FunctionName", Arguments);