Can't access property of Java Object passed to ScriptEngine

Question

I am passing an object "transformContext" from Java into a Graal.js scriptEngine. The object contains a Hashmap called "dataRecordsByName" which in Java I can usually access with the following line:

transformContext.get("dataRecordsByName")

I am attempting to retrieve the hashmap from the engine. I thought to do this I needed to replace the above line with:

engine.eval("transformContext.dataRecordsByName")

However this just returns undefined.

Here is my full code for this task:

ScriptEngine engine = new ScriptEngineManager().getEngineByName("graal.js");
engine.put("transformContext",transformContext);
engine.eval("console.log(transformContext)");
engine.eval("console.log(transformContext.dataRecordsByName)");

And here is the output to the console:

TransformContext(dataRecordsByName={$=[], CONVERSION=[{"From_Currency":"AUD","To_Currency":"AUD","Conversion_Rate":1.0,"historical_date":"31/05/2021","organisation_id":"ParentId","organisation_currency":"GBP","organisation_name":"Parent Id"}],...}, objectMapper=com.fasterxml.jackson.databind.ObjectMapper@21dfdc26)

undefined

Does anyone know why the engine is failing to retrieve the dataRecordsByName property?

Answer 1

After some further research it seems that graal.js does not map properties as I expected by default, but can do so if you run it in nashorn compatability mode.

System.setProperty("polyglot.js.nashorn-compat", "true");

After doing this, you can retrieve the object properties as you normally would in JavaScript:

engine.eval("console.log(transformContext.dataRecordsByName)");

Thanks to the guys on this thread: https://github.com/oracle/graaljs/issues/169