Can I invoke a function in a new engine scope with Nashorn?

Question

Nashorn allows me to evaluate a JavaScript in a new scope, like this:

public Object evalInNewScope(String code, Bindings bindings) throws Exception  {
    ScriptContext context = new SimpleScriptContext();
    context.setBindings(bindings, ScriptContext.ENGINE_SCOPE);
    return engine.eval(code, context);
}

This is great for thread-safety: The engine instance may be re-used across threads, and each thread can make its own call with thread-specific bindings.

However, I have not found a similar capability for Invocable#invokeFunction(String, Object...).

Does anyone know how I could do what I want? Is there a good reason for this asymmetry?

Answer 1

invokeFunction calls functions only from current context, you cannot provide a context directly.

ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("nashorn");

ScriptContext ctx = new SimpleScriptContext();
ctx.setBindings(engine.createBindings(), ScriptContext.ENGINE_SCOPE);
engine.eval("function hello() { return 'Hello!'; }", ctx);
engine.setContext(ctx);

((Invocable) engine).invokeFunction("hello");

Removing the engine.setContext(ctx) line would result in a java.lang.NoSuchMethodException: No such function hello exception.

Depending on your situation, you may have to re-set the original context!