How to get the attribute of a JS object from Java?

Question

I know I can use the Invocable class to invoke methods on a class:

import javax.script.{ScriptEngine, ScriptEngineManager, Invocable}

val engine = new ScriptEngineManager().getEngineByExtension("js")

val invoker = engine.asInstanceOf[Invocable]

val person = engine.eval(s"""
  new function () {
    this.name = "Rick";
    this.age = 28;
    this.speak = function () {
      return this.name + "-" + this.age;
    }
  };
""")

invoker.invokeMethod(person, "speak") //returns "Rick-28"

But, how do I get the name attribute of the person? I tried invoker.invokeMethod(person, "name") and I got a NoSuchMethodError.

I think you will have to "expose" all members you want to share with java part, aka create getters (and optionally setters). — Rafouille
– Rafouille, Commented Mar 2, 2016 at 9:03
You can try to assign the person to variable in JavaScript and use engine.get('person.name') — jcubic
– jcubic, Commented Mar 2, 2016 at 9:05
@awadheshv: person is an Object. It does not have .get. — pathikrit
– pathikrit, Commented Mar 2, 2016 at 9:23
@jcubic - yes that would work but I don't control the JS source in this case. We can invoke methods from Java, why not access members? — pathikrit
– pathikrit, Commented Mar 2, 2016 at 9:23

Raffaele · Accepted Answer · 2016-03-02 09:38:57Z

2

You can cast person to a JSObject and then call person.getMember("name"). Full Java example:

ScriptEngine engine = new ScriptEngineManager()
                           .getEngineByExtension("js");

JSObject rick = (JSObject) engine.eval("new function () {\n" +
        "            this.name = \"Rick\";\n" +
        "            this.age = 28;\n" +
        "            this.speak = function () {\n" +
        "                return this.name + \"-\" + this.age;\n" +
        "            }\n" +
        "        };");

System.out.println(rick.getMember("name"));

Or, if the object is stored in the engine global scope like in the following javascript source:

rick = function() {
  this.name= "Rick";
};

you can then call

engine.eval("rick.name");

answered Mar 2, 2016 at 9:38

Raffaele

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