Draft attempt to transpile vega 5 to ES2015 (or whatever will work)

Problem - Server Side Rendering of Vega Plots on Nashorn, JDK8

Do to external constraints, I’m trying to exploit server side rendering to headlessly emit SVG files from vega plots programmatically.

Node is not an option, but the JVM is.

• Oracle JRE8 222+ for deployment
• OpenJDK8 for dev
• GraalJS is not an option.

Attempts

I can get early versions of Vega 3 parsing and running with limited compatibility in Nashorn without modifications.

These understandably don’t render modern plots correctly, which we need to target Vega5.x for.

Vega 5 is largely ES6 or later, so we get parsing errors from Nashorn (even with es6 options enabled).

Use babel to transpile (recommended by vega)

So this brings us to babel. After following some tutorials, I managed to get the setup with the local package.json and a simple babel.config.js.

You’d invoke it as a build task from npm:

npm run build

This gets us a supposedly transpiled output. Nashorn then tries to load it, but I get parsing errors, e.g.

Execution error (ParserException) at jdk.nashorn.internal.runtime.Context$ThrowErrorManager/error (Context.java:437).
jdk.nashorn.internal.ir.FunctionNode cannot be cast to jdk.nashorn.internal.ir.Block

Previous experience leads me to believe this is Nashorn’s parser not recognizing stuff.

Rhino

I tried a similar path with Rhino. I ran into similar parsing problems though. I would be happy to have either Nashorn or Rhino work.

Questions

• What incantations are required to get Nashorn to even parse this?
• What additional presets/plugins or even hand crafted mods are required to get nashorn to evaluate the transpiled result?